The present invention provides a compound represented by formula (1) or a pharmaceutically acceptable salt of the compound. (In the formula, X and Y may be the same or different, and each represents a hydrogen atom, a halogen atom, a C1-6 alkyl group or a C1-6 alkoxy group, and the C1-6 alkoxy group may be substituted by a C1-6 alkoxy group； and Z and W may be the same or different, and each represents a hydrogen atom, a halogen atom or a C1-6 alkyl group.)
