A data reproducing circuit having a magnetic head for reading data from a recording medium, an adaptive equalization circuit for optimizing the waveform of a read signal, a discriminator circuit for discriminating an output signal of the adaptive equalization circuit and outputting a discriminated signal to an upper stage circuit, a format detecting circuit for detecting a pattern of signals written on the recording medium from outputs of the magnetic head, an expected value generating circuit for generating an expected value of the waveform of the read signal in accordance with an output of the adaptive equalization circuit and an output of the discriminator circuit, and an error detecting circuit for generating an error signal representing a difference between an output of the adaptive equalization circuit and an output of the expected value generating circuit. In the data reproducing circuit, the adaptive equalization characteristic of the adaptive equalization circuit is changed when a particular signal pattern on the recording medium is detected, allowing the adaptive equalization operation suitable for the recording medium.