Inclusion Criteria:
1. Subject has at least 16 points on Japanese version of the Children's Yale-Brown Obsessive Compulsive Scale 10-item total score and at least 5 points in Obsession sub-total score and in Compulsion sub-total score respectively at the Screening period and Baseline.
2. Subject showed less than 25% reduction in Japanese version of the Children's Yale-Brown Obsessive Compulsive Scale 10-item total score at Baseline compared to the score at the Screening period (Total score at Baseline ≥ Total score at Screening х 0.75).
3. Subject has obsessive compulsive disorder symptoms at least for 2 months at informed consent.
4. Body weight: ≥ standard weight - 2 standard deviation based on the standard weight for each age in the School Health Statistical Survey 2001.
5. Subjects with parent or legal guardian who have received explanation about the purpose, procedure and meaning of the study sufficiently and is willing to give written informed consent for the subject. (if possible, written informed assent will be obtained from the subject).
Exclusion Criteria:
1. Subject has only trichotillomania (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 312.39) or nail-biting as his/her compulsive symptoms.
2. Subject has Tourette's disorder (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 307.23). However, the simple motor tic is not excluded.
3. Subject is diagnosed with the following psychiatric disorders.
* Schizophrenia (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 295.xx) and other psychotic disorders (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 295.40 \[schizophreniform disorder\], 295.70 \[schizoaffective disorder\], 297.1 \[delusional disorder\], 298.8 \[brief psychotic disorder\], 297.3 \[shared psychotic disorder\], 293.xx \[psychotic disorder due to… {indicate the general medical condition}\], substance induced psychotic disorder, 298.9 \[psychotic disorder not otherwise specified\]).
* Depressive disorders Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 296.xx \[major depressive disorder\], 296.2x \[single episode\], 296.3x \[recurrent\], 300.4 \[dysthymic disorder\], 311 \[depressive disorder not otherwise specified\]).
* Bipolar disorders (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 296.xx \[bipolar I disorder\], 296.0x \[single manic episode\], 296.40 \[most recent episode hypomanic\], 296.4x \[most recent episode manic\], 296.6x \[most recent episode mixed\], 296.5x \[most recent episode depressed\], 296.7 \[most recent episode unspecified\], 296.89 \[bipolar II disorder\], 301.13 \[cyclothymic disorder\], 296.80 \[bipolar disorder not otherwise specified\]).
* Mental retardation (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 317 \[mild mental retardation\], 318.0 \[moderate mental retardation\], 318.1 \[severe mental retardation\], 318.2 \[profound mental retardation\], 319 \[mental retardation, severity unspecified\]).
* Eating disorders (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 307.1 \[anorexia nervosa\], 307.51 \[bulimia nervosa\], 307.50 \[eating disorder not otherwise specified\]).
* Attention-deficit/hyperactivity disorder (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 314.xx) and attention deficit/hyperactivity disorder not otherwise specified (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 314.9).
* Obsessive compulsive personality disorder (Diagnostic and Statistical manual of Mental Disorders Forth Edition Text Revision: 301.4).
* Other patients with clinical neurological disorder.
4. Subject who diagnose Major Depressive Disorder by The Mini-International Neuropsychiatric Interview for Children and Adolescents (A) at the Screening period.
5. Subject has been treated with fluvoxamine within 2 months prior to informed consent. Except for the patient whose fluvoxamine dose is not fixed and the administration period of fluvoxamine is within 6 weeks.
