The present invention provides a compound which has the effect of PDE inhibition, and which is useful as a medicament for preventing or treating schizophrenia or so on.A compound of formula (I0):whereinR1 representsa substituent,R2 representsa hydrogen atom, or a substituent,R3 representsa hydrogen atom, or a substituent,Ring A representsan aromatic ring which can be substituted, andRing B representsa 5-membered heteroaromatic ring which can be substituted,or a salt thereof.