An oil separator for separating mist oil contained in target gas, the oil separator comprising: a rotor that is rotatable together with a spindle and separates the mist oil by rotation; wherein the oil separator further comprises: a nozzle that is projected from a part of a peripheral surface of the spindle, the part being located below the rotor, and that injects oil from an injection hole to rotate the spindle around an axis; a housing including: an oil supply portion that supplies oil to be injected from the injection hole; oil communicating portions for discharging oil injected from the injection hole; and a gas communicating portion for introducing the target gas; wherein the oil communicating portions are disposed at positions that surround a support tube portion and the gas communicating portion; and a joint member that is removably mounted to the housing and includes a gas introducing portion and an oil discharge portion, the gas introducing portion introducing the target gas from outside and transferring the target gas to the gas communicating portion, the oil discharge portion receiving oil from the oil communicating portion and discharging the oil to outside. a rotor that is rotatable together with a spindle and separates the mist oil by rotation; wherein the oil separator further comprises: a nozzle that is projected from a part of a peripheral surface of the spindle, the part being located below the rotor, and that injects oil from an injection hole to rotate the spindle around an axis; a housing including: an oil supply portion that supplies oil to be injected from the injection hole; oil communicating portions for discharging oil injected from the injection hole; and a gas communicating portion for introducing the target gas; wherein the oil communicating portions are disposed at positions that surround a support tube portion and the gas communicating portion; and a joint member that is removably mounted to the housing and includes a gas introducing portion and an oil discharge portion, the gas introducing portion introducing the target gas from outside and transferring the target gas to the gas communicating portion, the oil discharge portion receiving oil from the oil communicating portion and discharging the oil to outside. a nozzle that is projected from a part of a peripheral surface of the spindle, the part being located below the rotor, and that injects oil from an injection hole to rotate the spindle around an axis; a housing including: an oil supply portion that supplies oil to be injected from the injection hole; oil communicating portions for discharging oil injected from the injection hole; and a gas communicating portion for introducing the target gas; wherein the oil communicating portions are disposed at positions that surround a support tube portion and the gas communicating portion; and a joint member that is removably mounted to the housing and includes a gas introducing portion and an oil discharge portion, the gas introducing portion introducing the target gas from outside and transferring the target gas to the gas communicating portion, the oil discharge portion receiving oil from the oil communicating portion and discharging the oil to outside. an oil supply portion that supplies oil to be injected from the injection hole; oil communicating portions for discharging oil injected from the injection hole; and a gas communicating portion for introducing the target gas; wherein the oil communicating portions are disposed at positions that surround a support tube portion and the gas communicating portion; and a joint member that is removably mounted to the housing and includes a gas introducing portion and an oil discharge portion, the gas introducing portion introducing the target gas from outside and transferring the target gas to the gas communicating portion, the oil discharge portion receiving oil from the oil communicating portion and discharging the oil to outside.