An analog input device to which an analog signal outputted from an external device can be inputted, for collecting the analog signal, comprising: a scanning circuit which includes a first insulation transformer for insulating the inputted analog signal; a power supply section for charging a test voltage used for detecting a disconnection caused in the external device; a second insulation transformer in which a switching input of scanning circuit is connected in parallel with the power supply section at the output side of the second insulation transformer; and control means for outputting a pulse signal to be inputted to the second insulation transformer, characterized in that: the second insulation transformer is adapted to receive a drive pulse for switching the scanning circuit from the control means and to insulate the drive pulse to send the drive pulse to the scanning circuit, and also to receive a power supply pulse for feeding power to the power supply section from the control means and to insulate the power supply pulse to send the power supply pulse to the power supply section; the scanning circuit comprises a rectifying element (31, 32) for preventing leakage current; and the control means is adapted to perform a timing control so that the drive pulse and the power supply pulse are not outputted at the same time, and to output the drive pulse and the power supply pulse therefrom. a scanning circuit which includes a first insulation transformer for insulating the inputted analog signal; a power supply section for charging a test voltage used for detecting a disconnection caused in the external device; a second insulation transformer in which a switching input of scanning circuit is connected in parallel with the power supply section at the output side of the second insulation transformer; and control means for outputting a pulse signal to be inputted to the second insulation transformer, characterized in that: the second insulation transformer is adapted to receive a drive pulse for switching the scanning circuit from the control means and to insulate the drive pulse to send the drive pulse to the scanning circuit, and also to receive a power supply pulse for feeding power to the power supply section from the control means and to insulate the power supply pulse to send the power supply pulse to the power supply section; the scanning circuit comprises a rectifying element (31, 32) for preventing leakage current; and the control means is adapted to perform a timing control so that the drive pulse and the power supply pulse are not outputted at the same time, and to output the drive pulse and the power supply pulse therefrom. the second insulation transformer is adapted to receive a drive pulse for switching the scanning circuit from the control means and to insulate the drive pulse to send the drive pulse to the scanning circuit, and also to receive a power supply pulse for feeding power to the power supply section from the control means and to insulate the power supply pulse to send the power supply pulse to the power supply section; the scanning circuit comprises a rectifying element (31, 32) for preventing leakage current; and the control means is adapted to perform a timing control so that the drive pulse and the power supply pulse are not outputted at the same time, and to output the drive pulse and the power supply pulse therefrom.