According to one embodiment, a circuit for generating a signal has an amplifier, first and second detection circuits, first and second A/D converters, and a digital signal processing circuit. The amplifier amplifies an electric signal corresponding to an intensity of a reflected light from an optical disc. The first detection circuit detects an upper envelope of an output signal from the amplifier, and outputs an upper envelope signal. The second detection circuit detects a lower envelope of an output signal from the amplifier, and outputs a lower envelope signal. The first A/D converter converts the upper envelope signal into a first digital signal. The second A/D converter converts the lower envelope signal into a first digital signal. The digital signal processing circuit performs calculation processing of the first and the second digital signals, and outputs a signal for controlling reproduction of data recorded on the optical disc.