Constitution: 1-Methylcarbapenem compounds of general formula (I) and pharmacologically acceptable salts and derivatives thereof, wherein R1 is hydrogen or lower alkyl; R2 is hydrogen or lower alkyl; and R3 is hydrogen, lower alkyl, substituted lower alkyl, cycloalkyl or -C(=NH)R4 (wherein R4 is hydrogen, lower alkyl or amino). Effect: these compounds exhibit excellent antibacterial activity and are useful as preventive or therapeutic agents for infectious diseases.