Provided is an oil feed type air compressor which can increase the determination accuracy regarding a deterioration state of oil. An oil feed type air compressor 1 includes a compressor main body 3, a separator 6 that separates oil from compressed air discharged from the compressor main body 3, and an oil feeding system 8 that feeds the oil separated by the separator 6 into a compression chamber of the compressor main body 3. The oil feeding system 8 includes a temperature control valve 20 that adjusts a diversion ratio for an oil cooler 18 and a diversion ratio for a bypass pipe 19 according to a temperature of the oil. The oil feed type air compressor 1 includes pressure sensors 22A and 22B located in the oil feeding system 8, a discharge temperature sensor 11 located on the discharge side of the compressor main body 3, and a controller 9 that computes, when it is estimated that the diversion ratio for the oil cooler 18 is 100% from the temperature sensed by the discharge temperature sensor 11 exceeding a predetermined value Td1, a difference ΔP between the pressure sensed by the pressure sensor 22A and the pressure sensed by the pressure sensor 22B and determines a deterioration state of the oil in reference to the difference ΔP.