The pistons in this reciprocating engine perform reciprocating motion inside of cylinders by means of the explosive pressure generated in a combustion chamber (124) formed inside of the cylinders (110). This reciprocating engine is provided with a liquid fuel supply unit (148) which supplies a liquid fuel to a combustion chamber, and a gas supply unit (a fuel gas supply unit (150), an EGR supply unit (152)) which supplies into the cylinder a combustion gas and an EGR gas, which is the exhaust gas discharged from the combustion chamber generated by combustion in the combustion chamber.