The present invention identifies a compound which binds to the PAH1 domain of mSin3B that specifically binds to neural restrictive silencer factor NRSF, and uses the compound as a prophylactic and/or a therapeutic for diseases associated with abnormal expression of neural restrictive silencer factor NRSF/REST or abnormal expression of genes targeted by NRSF/REST, such as Huntington's disease, medulloblastoma and neuropathic pain.The present invention provides a pharmaceutical composition comprising a substance capable of binding to the PAH1 domain of mSin3B, e.g., a compound represented by the following formula (1), a pharmacologically acceptable salt thereof, or a pharmacologically acceptable ester thereof: wherein n represents 0 or 1; R1, R2, R3, R4 and R5 each independently represent a hydrogen atom, a hydrocarbon group or a functional group; Y represents a single bond, a carbonyl group, —CONH—, —NHCO— or a sulfonyl group; and Z represents a nitrogen-containing heterocyclic group which may have a substituent, an amino group which may have a hydrocarbon group or an aromatic hydrocarbon group, or a nitrogen and oxygen-containing heterocyclic group which may have a substituent.