A state monitoring unit monitors a state of an assembled battery in which unit cells are connected in series. The state monitoring unit includes a plurality of voltage monitoring devices and a controller. The controller transmits a common voltage measurement command to the voltage monitoring devices connected in a daisy-chain scheme. Each of the voltage monitoring devices measures the voltage of the corresponding unit cells in response to the command that is received from the controller or the adjacent voltage monitoring device at a leading end of the communication channel, and transmits the command to the adjacent voltage monitoring device at a termination of the communication channel. When received the measured voltage from the adjacent voltage monitoring device at the termination, the voltage monitoring device transmits it with the own measured voltage. The controller determines the abnormality in reception state based on the number of received, measured voltages.