An oil separator causes air containing oil to strike an impingement member to separate the oil from the air and recover the oil. The oil separator includes a body having an inlet for introducing air and an outlet for discharging air. The oil separator further includes a cartridge that is assembled to the body and accommodates the impingement member. The oil separator further includes a drain bowl for storing the separated oil. The oil separator further includes an assembling structure. The body and the cartridge are assembled through one or two actions by using the assembling structure.