A cam driving device for a processing device including a cylindrical member, a rotational shaft that has a mount hole formed on the outer peripheral surface thereof, a cam, and a tool that is mounted in the mount hole of the cylindrical member so that the tool can be protruded and retracted through the mount hole in a radial direction of the rotational shaft in accordance with a profile of the cam. The cylindrical member and the rotational shaft are axially reciprocated to process a non-circular bore, including a storage unit for storing a data table representing associating relationship between a rotational angle of the cam and a protrusion amount of the tool which is provided on the basis of the rotational angle of the cam, and a controller for advancing or retarding the rotational angle of the rotational shaft according to the data table stored in the storage unit.