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), wherein R1 represents a substituent; R2 represents a hydrogen atom, or a substituent; R3 represents a hydrogen atom, or a substituent; Ring A represents an aromatic ring which can be substituted, and Ring B represents a 5-membered heteroaromatic ring which can be substituted, or a salt thereof.