An analog-to-digital conversion device includes: a switch connected to input units through signal lines to receive external voltages selecting and outputting one external voltage; an S/H circuit holding a voltage corresponding to an output of the switch; a converter performing AD conversion based on the voltage; and a controller determining the external voltage selected by the switch and performing a disconnection determination whether a disconnection occurs in the signal line. In the disconnection determination, the controller controls the switch to select a reference voltage different from the external voltage before controlling the switch to select the external voltage to be determined, and performs the disconnection determination based on a voltage difference between the reference voltage and the external voltage after controlling the switch to select the external voltage.