A lap (201) of an orbiting scroll (21) and a lap (202) of a stationary scroll (22) are meshed with each other to form an inner wall side expansion chamber (203a) on the side of a lap inner wall (201a) of the orbiting scroll (21) and an outer wall side expansion chamber (203b) on the side of a lap outer wall (201a) of the orbiting scroll (21). The volumetric capacity of the inner wall side expansion chamber (203a) and that of the outer wall side expansion chamber (203b) are equal to each other when suction is completed, and different from each other when discharge starts, and their expansion ratios are different from each other.