PURPOSE: To detect an accurate rainfall state by performing the composite processing of the detection output of a liquid detection sensor as to whether it rains or not and the detection output of a pressure sensor as to the degree of rainfall and outputting the result on a display device.

CONSTITUTION: When it beings to rain and water drops strike on a sensor part 1 installed outdoors, the liquid detection sensor 5 detects whether there is a water drop or not and the pressure sensor 4 detects the strength of striking of water drops and the number of drops. The detection outputs of those sensors 4 and 5 are converted and transmitted through a communication circuit 8. The information which is transmitted from the sensor part 1 is inputted to a microcomputer 10 through a modem 9 and processed so that it is displayed on a screen suitably, thereby displaying the information on the CRT display screen 11. Consequently, the presence/absence state of rain and the degree of rainfall are displayed stepwise and an accurate judgement is made in a room without looking out of a window actually.