The present invention deals relates to vane pump with variable discharge volume, comprising: a pump housing; a cam ring having an elliptical cross-section for its inner circumference and outer circumference to form a compression chamber wherein a compression medium is compressed, and is accommodated in said pump housing so that it may rotate; a rotor that is accommodated such that a plurality of vanes may appear frequently on the outer circumference to undergo rotations in the compression chamber of said cam ring and compress said compression medium; and a cam ring rotation controller that contacts the outer circumference of said cam ring, and rotates said cam ring if the discharge pressure of said compression medium is equal to or more than its pressure setting and stops the rotation of said cam ring if the discharge pressure of said compression medium is less than its pressure setting to control rotations of said cam ring. Accordingly, the rotation and stoppage of rotation of the cam ring is accomplished based on changes in the discharge pressure, to enable variation in discharge volumes, and enhancement of discharge efficiency.