Deterioration of error rate at reproduction time is prevented even if a photodetector with a poor characteristic is included. An optical pickup unit (3) is provided with 4 photodetectors. A controller (13) obtains an error correction result of a reproduced signal, which is reproduced based on an RF signal generated while changing combination of the 4 photodetectors at startup time, and determines a combination at reproduction time in accordance with the obtained error correction result, to be given to an RF amplifier unit (10). The controller (13) is provided with a counter that counts for a fixed time period the error correction result per combination of the photodetectors, a comparator that compares a count result of the counter with a threshold set in advance, and an output controller that judges whether or not to use a combination of the photodetectors based on a comparison result of the comparator and performs change control of the combination of the photodetectors, of which there is a plurality. At reproduction time, control is performed to obtain the reproduced signal from output outside of the photodetector with the poor characteristic.