To provide an oil separator capable of promoting improvement in oil separation efficiency while suppressing an increase in cost.

In an oil separator 20 including a device body 21 which has a cylindrical trunk part 211 and in which an upper end opening and lower end opening of the trunk part 211 are respectively closed by an upper lid 212 and a lower lid 213, and an introduction pipe 22 which is connected to a side face of the trunk part 211 such that its central axis L2 horizontally deviates from a central axis L1 of the trunk part 211 to introduce an oil mixed refrigerant into the device body 21, centrifugally separating the oil mixed refrigerant introduced through the introduction pipe 22 into the refrigerant and oil by turning it around the central axis L1 within the trunk part 211, discharging the refrigerant through a refrigerant discharge pipe 23 connected to the upper lid 212, and discharging the oil through an oil discharge pipe 24 connected to the lower lid 213, a curvature of an inner wall surface 222 of the introduction pipe 22 on a side separating from the central axis L1 is formed larger than that of an inner wall surface 221 on a side approaching the central axis L1 of the trunk part 211.