A multilevel input interface device connected to a signal bus including one or more data lines that transmit an M-level signal and a clock line that transmits a transmission clock signal indicating the timings of reading level information for the M-level signal, includes: a threshold value generation unit that produces a plurality of voltage outputs as a plurality of variable comparison reference signals according to the level-varying supply voltage; a level detection unit that compares, in synchronization with the transmission clock signal, the M-value level signal with the variable comparison reference signals and generates a logic output corresponding to an instantaneous value of the M-level signal; and a logic circuit unit that converts the logic output to a data signal.