The present invention provides a sterilizer which includes a steam chamber comprising a steam chamber upper member (201) and a steam chamber lower member (202) which are bolt-coupled to each other; an inlet door (110) configured to open or close an inlet (210) of the steam chamber; and an outlet door (120) configured to open or close an outlet (220) of the steam chamber, wherein each of the steam chamber upper member (201) and the steam chamber lower member comprises a housing (241, 242) defining a steam chamber inner space and a plurality of reinforcement ribs (251, 252) formed on a surface of the housing at a predetermined height.