This invention relates to compounds (I) or pharmaceutically acceptable salts thereof, having a function to inhibit type IV phosphodiesterase (PDE) ##STR1## [X: an oxygen atom or a sulfur atom, R.sup.1 : a lower alkyl group, a cycloalkyl-lower alkyl group or a cycloalkyl group,R.sup.2 : a hydrogen atom, a halogen atom, a lower alkyl group, a halogeno-lower alkyl group, a hydroxy-lower alkyl group, a mercapto-lower alkyl group, a lower alkoxy-lower alkyl group, a lower alkylthio-lower alkyl group, a lower alkanoyloxy-lower alkyl group, a lower alkanoylthio-lower alkyl group, a lower alkanoyl-lower alkyl group, a hydroxyimino-lower alkyl group, a lower alkoxyimino-lower alkyl group, a cycloalkyl group, an aryl group or a lower alkanoyl group,R.sup.3 : a hydrogen atom, a halogen atom or a lower alkyl group,R.sup.4 : a hydrogen atom or a lower alkyl group,R.sup.5 : a cycloalkyl group; a naphthyl group substituted; a five- or six-membered monocyclic hetero ring group having 1 to 4 hetero atoms selected from nitrogen atom, oxygen atom and sulfur atom; or a group represented by the formula ##STR2## amd F.sup.6 : a halogen atom, a lower alkyl group, a halogeno-lower alkyl group, a hydroxyl group, a lower alkoxy group, a cyano group or a nitro group].