It is to provide a novel pyrazolone derivative represented by the following general formula (1), which is useful as a pharmaceutical and has a phosphodiesterase inhibitory action: ##STR00001## wherein R.sup.1,R.sup.2: C.sub.1-6 alkyl; R.sup.3,R.sup.4: H, X, C.sub.1-6 alkoxy; Z:O, S; A:AA, BB,wherein AA represents ##STR00002## wherein BB represents ##STR00003## wherein R.sup.5: H, C.sub.1-6 alkyl; R.sup.6,R.sup.7: C.sub.1-6 alkyl.