Provided is a signal processing device including a signal receiving unit for receiving a multilevel signal having a signal waveform that is obtained by synchronously adding an encoded signal generated based on a specific coding rule and a clock which has an amplitude larger than the encoded signal and for which the transmission speed is half that of the encoded signal, an amplitude level detection unit for detecting an amplitude level of the multilevel signal received by the signal receiving unit, a violation detection unit for detecting a bit position at which rule violation of the specific coding rule occurred, based on a change pattern of the amplitude level detected by the amplitude level detection unit, and an error correction unit for correcting a detection value of the amplitude level corresponding to the bit position detected by the violation detection unit so that the rule violation is resolved.