An apparatus for processing a sample using microwaves comprises: a reaction vessel comprising a chamber which accommodates a refrigerant and a sample and an injection port through which a gas is injected; a microwave source which irradiates microwaves into the chamber; a connector which carries the gas injected through the injection port; and a gas supplier which is located in the chamber and injects the gas carried by the connector to a refrigerant in the chamber. The connector may comprise a gas carrying portion located above the level of the refrigerant in the chamber.