A medicament having an inhibitory activity against hematopoietic prostaglandin D2 synthase, which comprises as an active ingredient a compound represented by the following general formula (I) or a salt thereof:
wherein X represents a group represented by the formula —N═C(R
5
)— or the formula —NH—CH(R
5
)—, R
1
, R
2
, R
3
, and R
4
represent a hydrogen atom, a halogen atom, a C
1
to C
6
alkyl group, or a hydroxy group, R
5
represents a C
1
to C
6
alkyl group or a C
6
to C
10
aryl group, and R represents an amino group.