A 1-cycloalkyl-1,8-naphthylidin-4-one derivative having the formula (I): wherein R1 indicates a substituted or unsubstituted cycloalkyl group or a substituted or unsubstituted heterocycloalkyl group, R2, R3, and R4 independently indicate a hydrogen atom, a substituted or unsubstituted lower alkyl group, or a halogen atom, X indicates a group NR5R6 or a group OR7, wherein R5 and R6 independently indicate a hydrogen atom, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group, and R7 indicates a hydrogen atom, a substituted or unsubstituted lower alkyl group, or a substituted or unsubstituted cycloalkyl group or a pharmaceutically acceptable salt or solvate thereof and a type IV phosphodiesterase inhibitor containing the same as an effective component.