To simply perform proper management by informing a manager by a sensor attached to each set position of the lower limit and the upper limit of an underground water level, forwarding it to a next manager in the case where the manager is absent and interrupting forwarding at the time when information is received.

When underground water is pumped by a submergible pump 3 and lost, an OFF sensor S1 arranged at an excavation bottom face position detects it, and transmits it from a communication line 7 to an informing device 6. In addition, when an underground water level reaches an upper limit position, an ON sensor S2 arranged at the upper limit position of the underground water level detects it, and transmits it from the communication line 7 to the informing device 6. A transmission sound from the sensors S1, S2 is received by the informing device 6, and transmitted to the receiver 8 of a manager. Furthermore, in the case where the manager is absent or communication is impossible, it is automatically forwarded to a next manager, and at the time when information is received, forwarding is interrupted. Thereby the proper management of the underground water level can be performed by a simple method.