PURPOSE: To confirm normal operation without the need to raise the level of a substance until coming into an excessively filled state.

CONSTITUTION: A device for testing an equipment system includes a test signal generator 34 which is coupled with an equipment output transmission line 30 at a distance from an equipment 22. A test signal is received by a test signal receiver 28 coupled with the transmission line nearby the equipment 22, which is then supplied with a signal simulating a signal supplied from a sensor 20 to the equipment 22 under certain conditions, so that the dummy signal generates an equipment output signal corresponding to the remote position as long as the whole system operates normally.