A battery voltage monitoring device for monitoring an output voltage of a unit cell or unit cells in each of battery modules (M1-Mn) that are connected in series, comprising: integrated circuits (CC1-CCn), each of which samples and holds the output voltage of the unit cell or unit cells in each of the battery modules (M1-Mn); a cascade communication circuit that connects the integrated circuits (CC1-CCn) in series to transmit signals to the integrated circuits (CC1-CCn) according to a connection order of the integrated circuits (CC1-CCn); and a programmable controller connected to an integrated circuit (CC3, CCn) located at an upstream end of the cascade communication circuit and an integrated circuit located at a downstream end of the cascade communication circuit with respect to signal transmission; wherein the controller is programmed to: output a voltage sampling and holding command signal to the integrated circuit (CC3, CCn) at the upstream end such that the voltage sampling and holding command signal be transmitted to each of the integrated circuits (CC1-CCn) via the cascade communication circuit, the voltage sampling and holding command signal commanding each of the integrated circuits (CC1-CCn) to sample and hold output voltage of the unit cell or unit cells in each of the battery modules (M1-Mn); and output a transmission command signal to the integrated circuit (CC3, CCn) at the upstream end such that the transmission command signal be transmitted via the the cascade communication circuit to each of the integrated circuits (CC1-CCn) after transmission of the voltage sampling and holding command signal, the transmission command signal commanding each of the integrated circuits (CC1-CCn) to transmit output voltage held by each of the integrated circuits (CC1-CCn) to the controller via the cascade communication circuit, characterized in that the controller is further programmed to determine if the voltage sampling and holding command signal has reached the integrated circuit at the downstream end and not to output the transmission command signal until the voltage sampling and holding command signal reaches the integrated circuit at the downstream end. integrated circuits (CC1-CCn), each of which samples and holds the output voltage of the unit cell or unit cells in each of the battery modules (M1-Mn); a cascade communication circuit that connects the integrated circuits (CC1-CCn) in series to transmit signals to the integrated circuits (CC1-CCn) according to a connection order of the integrated circuits (CC1-CCn); and a programmable controller connected to an integrated circuit (CC3, CCn) located at an upstream end of the cascade communication circuit and an integrated circuit located at a downstream end of the cascade communication circuit with respect to signal transmission; wherein the controller is programmed to: output a voltage sampling and holding command signal to the integrated circuit (CC3, CCn) at the upstream end such that the voltage sampling and holding command signal be transmitted to each of the integrated circuits (CC1-CCn) via the cascade communication circuit, the voltage sampling and holding command signal commanding each of the integrated circuits (CC1-CCn) to sample and hold output voltage of the unit cell or unit cells in each of the battery modules (M1-Mn); and output a transmission command signal to the integrated circuit (CC3, CCn) at the upstream end such that the transmission command signal be transmitted via the the cascade communication circuit to each of the integrated circuits (CC1-CCn) after transmission of the voltage sampling and holding command signal, the transmission command signal commanding each of the integrated circuits (CC1-CCn) to transmit output voltage held by each of the integrated circuits (CC1-CCn) to the controller via the cascade communication circuit, output a voltage sampling and holding command signal to the integrated circuit (CC3, CCn) at the upstream end such that the voltage sampling and holding command signal be transmitted to each of the integrated circuits (CC1-CCn) via the cascade communication circuit, the voltage sampling and holding command signal commanding each of the integrated circuits (CC1-CCn) to sample and hold output voltage of the unit cell or unit cells in each of the battery modules (M1-Mn); and output a transmission command signal to the integrated circuit (CC3, CCn) at the upstream end such that the transmission command signal be transmitted via the the cascade communication circuit to each of the integrated circuits (CC1-CCn) after transmission of the voltage sampling and holding command signal, the transmission command signal commanding each of the integrated circuits (CC1-CCn) to transmit output voltage held by each of the integrated circuits (CC1-CCn) to the controller via the cascade communication circuit, characterized in that the controller is further programmed to determine if the voltage sampling and holding command signal has reached the integrated circuit at the downstream end and not to output the transmission command signal until the voltage sampling and holding command signal reaches the integrated circuit at the downstream end.