A cyclopropane compound represented by the following formula (A) or a pharmaceutically acceptable salt thereof has orexin receptor antagonism, and therefore has a potencial of usefulness for the treatment of sleep disorder for which orexin receptor antagonism is effective, for example, insomnia:wherein Q represents -CH- or a nitrogen atom, R1a and R1b each independently represent a C1-6 alkyl group and the like, R1c represents a hydrogen atom and the like, R2a, R2b, R2c and R2d each independently represent a hydrogen atom, a halogen atom, a Cl-6 alkyl group and the like, R3a, R3b and R3c each independently represent a hydrogen atom, a halogen atom and the like, and R3d represents a hydrogen atom and the like.本發明揭露一種藉由下式(A)表示之環丙烷化合物或其藥學上可接受的鹽類，其具有食慾素(orexin)受體拮抗作用，且因此具有用於睡眠障礙治療之有用性的濳力，對該睡眠障礙而言，食慾素(orexin)受體拮抗作用是有效的，例如失眠症(insomnia)：其中Q表示-CH-或氮原子，R1a及R1b各自獨立地表示C1-6烷基及類似基團，R1c表示氫原子及類似原子，R2a、R2b、R2c及R2d各自獨立地表示氫原子、鹵素原子、C1-6烷基及類似基團，R3a、R3b及R3c各自獨立地表示氫原子、鹵素原子及類似原子，以及R3d表示氫原子及類似原子。
