A compound represented by formula (A) [wherein Q represents -CH- or a nitrogen atom； R1a and R1b independently represent a C1-6 alkyl group or the like； R1c represents a hydrogen atom or the like； R2a, R2b, R2c and R2d independently represent a hydrogen atom, a halogen atom or the like； R3a, R3b and R3c independently represent a hydrogen atom, a halogen atom or the like； and R3d represents a hydrogen atom or the like] or a pharmaceutically acceptable salt thereof, which has an antagonistic activity on an orexin receptor, and therefore can be used as a therapeutic agent for sleep disorders, such as insomnia, on which the antagonistic activity on an orexin receptor is effective.
