An oil separator comprising: a cylindrical container body into which a liquid mixture of a refrigerant and a refrigeration oil flows; an injection pipe inserted into the container body from an insertion port formed in a sidewall of the container body, and introducing the liquid mixture into the container body; and a refrigerant discharge pipe vertically disposed in an upper portion of the container body, allowing the refrigerant of the liquid mixture to flow out of the container body, and having a lower end which serves as an inlet end of the refrigerant and which is disposed below the injection pipe, wherein the injection pipe has a bend disposed inside the container body and bent such that an outer portion of the bend is closer to the sidewall of the container body than an inner portion of the bend is when the container body is viewed from above, wherein the injection pipe further includes an extension extending substantially linearly from the insertion port to the bend inside the container body, and the bend is disposed opposite to the insertion port with respect to a first reference plane including a central axis of the container body and substantially orthogonal to the extension and characterized in that a distance X defined by a length of a straight line connecting a center of the inner diameter of the extension to an outlet end of the injection pipe is determined so as to satisfy the following expression based on a curvature radius r of the inner portion of the bend: 2.5 × r ≤ X ≤ 3.5 × r, and the outlet end of the injection pipe is disposed in a region opposite to a region (arl), which is inside the container body and includes the extension, with respect to a second reference plane including the central axis of the container body and substantially parallel to the extension. a cylindrical container body into which a liquid mixture of a refrigerant and a refrigeration oil flows; an injection pipe inserted into the container body from an insertion port formed in a sidewall of the container body, and introducing the liquid mixture into the container body; and a refrigerant discharge pipe vertically disposed in an upper portion of the container body, allowing the refrigerant of the liquid mixture to flow out of the container body, and having a lower end which serves as an inlet end of the refrigerant and which is disposed below the injection pipe, wherein the injection pipe has a bend disposed inside the container body and bent such that an outer portion of the bend is closer to the sidewall of the container body than an inner portion of the bend is when the container body is viewed from above, wherein the injection pipe further includes an extension extending substantially linearly from the insertion port to the bend inside the container body, and the bend is disposed opposite to the insertion port with respect to a first reference plane including a central axis of the container body and substantially orthogonal to the extension and characterized in that a distance X defined by a length of a straight line connecting a center of the inner diameter of the extension to an outlet end of the injection pipe is determined so as to satisfy the following expression based on a curvature radius r of the inner portion of the bend: 2.5 × r ≤ X ≤ 3.5 × r, and the outlet end of the injection pipe is disposed in a region opposite to a region (arl), which is inside the container body and includes the extension, with respect to a second reference plane including the central axis of the container body and substantially parallel to the extension.