The present invention provides a compound which has the effect of PDE inhibition, and which is useful as an agent for preventing or treating schizophrenia. The compound is represented by the formula (I): wherein the symbols are defined in the specification.본 발명은 하기 화학식 (I) 로 나타내는, 정신분열증의 예방 또는 치료제로서 유용하며 PDE 저해 효과를 갖는 화합물 등을 제공한다: