The present invention achieves higher precision and lower power consumption by reducing semiconductor chip occupation area. A semiconductor integrated circuit which can be mounted on an optical disk device has: a wobble signal generating circuit capable of receiving first, second, third, and fourth light reception output signals A, B, C, and D of a light receiving element in an optical pickup and detecting a wobble in a recordable disk; a differential phase detection signal (DPD) generating circuit for tracking an unrecordable disk; and two A/D converters and an arithmetic circuit. The first, second, third, and fourth light reception output signals are selectively supplied to the two A/D converters, the arithmetic circuit in a first operation mode generates a first addition output signal of A and C and a second addition output signal of B and D, the DPD generating circuit generates a digital phase comparison signal, the arithmetic circuit in a second operation mode generates a third addition output signal of A and D and a fourth addition output signal of B and C, and the wobble signal generating circuit generates a digital wobble signal.