To provide a compressor with a BOG (Boil Off Gas) warmer, whose cost can be reduced by reducing the thermal load of a BOG compressor.

The compressor with the BOG warmer comprises the BOG compressor 3 for sucking and compressing BOG generated in a power generation system using LNG as fuel to increase the pressure, and then mixing it with the LNG vaporized via a vaporizer 2, and the BOG warmer 7 arranged at the front stage of the BOG compressor 3 for heat exchange with heat medium as cooling water to be used in the power generation system to increase the pressure of the BOG.