A discrete Fourier transform circuit (201) calculates a first frequency spectrum in a predetermined frequency range from a detection signal in a predetermined segment. An expectation calculation circuit (202) calculates a second frequency spectrum corresponding to an expectation signal of a pattern of digital information that is present in the predetermined segment and obtained via an optical disc (100). A branch metric calculation circuit (203) calculates a difference between the first frequency spectrum and the second frequency spectrum. A maximum likelihood decoding circuit (207) decodes the digital information by selecting a pattern in which the difference between the first frequency spectrum and the second frequency spectrum is minimized as a decoding result.