A cam driving mechanism has: a cam; a motor which drives the cam; a gear train which transmits, while reducing the speed of, the output of the motor to the cam; a pulse disk which is formed integrally with a gear coupled in the gear train and in which a plurality of slits are formed at equal intervals; a home position detecting member which is arranged coaxially with the pulse disk so as to be rotatable independently thereof and which, by meshing with another gear coupled in the gear train, rotates at a lower rotation speed than the pulse disk; and a cam position detecting sensor which has a detecting portion including a light-emitting portion and a light-receiving portion, the cam position detecting sensor detecting the amount of driving of the cam based on the number of slits of the pulse disk that have passed through the detecting portion, the cam position detecting sensor detecting the home position of the cam based on the timing with which the home position detecting member shields the detecting portion.