Four avian pneumovirus (APV) isolates from chickens clinically diagnosed with swollen head syndrome were genetically characterized as to the subtypes of the virus in Japan. The results of reverse transcriptase-polymerase chain reactions based on subtype-specific primers and direct sequence analysis of G genes indicated subtypes A and B but not C or D of APV were present in Japan. Several routes or sources are conceivable for APV to invade into Japan.