A standard signal generator adapted to generate a reference flow rate signal for calibrating an electromagnetic flowmeter, comprising: an input circuit configured to receive an excitation current obtained from a converter in the electromagnetic flowmeter; a battery holder to hold a battery; a power supply voltage source switching unit (31a, SW1) configured to switch a source of a power supply voltage to be used in the standard signal generator; and a remaining capacity indicator (31a, 33) configured to provide a remaining battery capacity indication, wherein the input circuit includes a rectifier circuit configured to rectify the excitation current obtained from the converter, and a constant voltage circuit configured to receive as input an output voltage of the rectifier circuit and control a power supply voltage output from a power supply voltage output terminal of the input circuit so that the power supply voltage is maintained constant, wherein the power supply voltage source switching unit (31a, SW1) is further configured to switch the source of the power supply voltage to be used in the standard signal generator to the constant voltage circuit when the converter, which is connected to the standard signal generator, is a converter of a four-wire electromagnetic flowmeter, and switches the source of the power supply voltage to be used in the standard signal generator to the battery placed in the battery holder when the converter, which is connected to the standard signal generator, is a converter of a two-wire electromagnetic flowmeter, wherein the remaining capacity indicator (31a, 33) is further configured to measure a voltage of the battery across electrodes of the battery holder, and provide a remaining battery capacity indication based on a measurement result obtained by measuring the voltage of the battery, and wherein when the converter, which is connected to the standard signal generator, is a converter of a four-wire electromagnetic flowmeter and it is determined, based on the measurement result, that the battery is not in the battery holder, the remaining capacity indicator (31a, 33) is configured to stop providing a remaining battery capacity indication. an input circuit configured to receive an excitation current obtained from a converter in the electromagnetic flowmeter; a battery holder to hold a battery; a power supply voltage source switching unit (31a, SW1) configured to switch a source of a power supply voltage to be used in the standard signal generator; and a remaining capacity indicator (31a, 33) configured to provide a remaining battery capacity indication, wherein the input circuit includes a rectifier circuit configured to rectify the excitation current obtained from the converter, and a constant voltage circuit configured to receive as input an output voltage of the rectifier circuit and control a power supply voltage output from a power supply voltage output terminal of the input circuit so that the power supply voltage is maintained constant, wherein the power supply voltage source switching unit (31a, SW1) is further configured to switch the source of the power supply voltage to be used in the standard signal generator to the constant voltage circuit when the converter, which is connected to the standard signal generator, is a converter of a four-wire electromagnetic flowmeter, and switches the source of the power supply voltage to be used in the standard signal generator to the battery placed in the battery holder when the converter, which is connected to the standard signal generator, is a converter of a two-wire electromagnetic flowmeter, a rectifier circuit configured to rectify the excitation current obtained from the converter, and a constant voltage circuit configured to receive as input an output voltage of the rectifier circuit and control a power supply voltage output from a power supply voltage output terminal of the input circuit so that the power supply voltage is maintained constant, wherein the power supply voltage source switching unit (31a, SW1) is further configured to switch the source of the power supply voltage to be used in the standard signal generator to the constant voltage circuit when the converter, which is connected to the standard signal generator, is a converter of a four-wire electromagnetic flowmeter, and switches the source of the power supply voltage to be used in the standard signal generator to the battery placed in the battery holder when the converter, which is connected to the standard signal generator, is a converter of a two-wire electromagnetic flowmeter, wherein the remaining capacity indicator (31a, 33) is further configured to measure a voltage of the battery across electrodes of the battery holder, and provide a remaining battery capacity indication based on a measurement result obtained by measuring the voltage of the battery, and wherein when the converter, which is connected to the standard signal generator, is a converter of a four-wire electromagnetic flowmeter and it is determined, based on the measurement result, that the battery is not in the battery holder, the remaining capacity indicator (31a, 33) is configured to stop providing a remaining battery capacity indication.