PROBLEM TO BE SOLVED: To provide a method for detecting an interference-type optical information signal capable of easily adjusting an optical path difference between signal light and reference light, providing a high signal amplification effect, and stably maintaining the effect, and suited to the miniaturization of an optical system. SOLUTION: The optical disk device for interfering light used as reference light without being applied to an optical disk 109 with reflected light from the optical disk, and obtaining an amplifying signal by calculation based on a plurality of interference signal outputs includes, in its signal processing circuit 25, a calculation adjustment mechanism for monitoring one or both of ongoing calculation and a calculation output and adjusting calculation so as to stabilize the output. Thus, variations of device components or an influence of a change of characteristics with time or the like is prevented, and an amplifying effect is stably obtained. COPYRIGHT: (C)2010,JPO&INPIT