Quantization noise due to analog-to-digital conversion may be larger than a noise component of an input signal, and therefore sufficient performance may not be obtained. An optical disk device includes an optical head for reading a signal recorded in an optical disk, an analog equalization circuit having an equalization characteristic that amplifies a predetermined frequency band of a signal read by the optical head, a converter for converting a signal equalized by the analog equalization circuit into a digital signal, a digital equalization circuit for adjusting a frequency characteristic of a signal digitized by the converter, a detector for detecting a level of a signal having minimum length in the signal digitized by the converter, and a decoding circuit that decodes a signal equalized by the digital equalization circuit using a maximum likelihood decoding method, wherein the analog equalization circuit has an equalization characteristic of amplifying a frequency corresponding to the signal having the minimum length in the signal recorded in the optical disk.