PURPOSE: To form the internal periphery shape of a cam ring by forcing a shaft head to vertically move while cutting the internal periphery of a workpiece mounted on a fixed base, in a method for manufacturing the peripheral shape of the cam ring of a vane pump.

CONSTITUTION: Assuming respective pitch circle radii of a fixing gear 11 and a planetary gear 13 attached to the shaft head of a machining tool to be respectively r, 2r, both gears turn in the same direction when turned with a carrier 12 fixed, so that three vertical shafts 11, 12, 13 are equally spaced, and when each gear moves with turning motion, its outer peripheral length becomes the same. Then, a cutting tool 15 is, since it is fixed on the gear 13 and turns together therewith, turned by θ around an A point, a locus drawn with its cutting operation coinsides with an evaluated value from a mathematical formula. Accordingly, driving the carrier 12 by means of the turning shaft 12a and vertically moving the shaft head 11 causes the tool 15 to machine a workpiece 4 to form the internal periphery 4a of the cam ring.