To effectively apply the hydraulic pressure supplied to the vane groove to the direction for projecting the vane even in the case a vane is completely embedded in a vane groove in a gas compressor.

A vane 58 has a notch 58c formed only in a part of its embedded side end face 58a. In the notch 58c, a face (face to receive hydraulic pressure applied in the direction for projecting the vane 58 toward a cylinder 40) 58d is formed facing the bottom face 56a of a vane groove 56. A gap 58c is formed between the bottom face 56a of the vane groove 56 and the face 58d of the vane 58 even at a position with the vane 58 embedded most deeply in the vane groove 56 so that the hydraulic pressure of a refrigerating machine oil R supplied to the vane groove 56 is effectively applied to the face 58d of the vane 58 via the gap 58c.