To provide a measuring unit for measuring temperature, etc., small in size, superior in weatherability such as waterproofness, small in power consumption and to capable of measuring for a long time.

The temperature measuring unit 10 is constituted by housing a thermistor 21 or a memory 22 for temperature measurement inside a miniaturized and sealed housing 19, and an input/output part 30 is provided for outputting data while using optical communication. Further, a phototransistor 32 for brightness/darkness sensing is provided so as to enable the optical communication when a communication unit 50 gets closer and it gets dark around the input/output part 30. Thus, since the power consumption at an interface for performing the optical communication can be reduced, temperature can be measured for a long time.