In a device for detecting errors in a charging line, the device detects an error in the charging line connecting the vehicle generator and an on-board battery. The device includes a bias circuit, a charging line error detecting means, and a warning means. The bias circuit biases a voltage of an external terminal receiving the power generation instruction signal in the vehicle power generation controller with a voltage of an output terminal of the vehicle generator. The charging line error detecting means detects the error in the charging line based on a voltage of an output terminal of the power generation instructing means that is provided within the external controller and generates the power generation instruction signal and a terminal voltage of the on-board battery. When the charging line error detecting means detects the error in the charging line, the warning means performs a warning operation to give notification of the error.