An evaporator includes a housing in which an evaporator chamber configured to evaporate a refrigerant is formed; a heat transfer surface provided on an inner wall of the housing and having a hot area which is a part that becomes hot due to heat transferred from a heating element to the housing; and a supply port formed in the housing, opposed to the hot area and configured to eject the refrigerant supplied from a supply pipe to the hot area, wherein a narrow groove is formed in the heat transfer surface.