Abstract: Novel pyrazolopyridylpyridazinone derivatives characterized by being represented by general formula (1) and pharnacologically acceptable salts thereof, which exhibit a phosphodiesterase inhibiting activity and have a selective potent bronchodilating effect on the respiratory tract; a process for the preparation of them; and bronchodilators containing the same as the active ingredient; wherein R1 is C1-C4 lower alkyl or C3-C6 cycloalkyl; and R2, R3, R4 and R5 are each independently hydrogen, C1-C4 lower alkyl or phenyl, or alternatively R3 and R5 may be united to form a double bond.