A method for treating glaucoma or ocular hypertension comprising administering to a patient a pharmacologically effective amount of a compound represented by the following (1) or a salt thereof: wherein X represents CH or N; R1 represents a hydrogen atom, a hydroxy group, a halogen atom, an alkyl group, an alkoxy group, a cycloalkyl group, a cycloalkoxy group, a (cycloalkyl)methoxy group, or  R2 represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkylcarbonyl group or an alkyloxycarbonyl group; and Ra and Rb are the same or different and represent a hydrogen atom, a hydroxy group, a halogen atom, an alkyl group, an alkoxy group, a cycloalkyl group or a cycloalkoxy group.