NOVELTY - The environment sensor e.g. humidity sensor (100) has a sensor portion (10) that detects specific physical quantity in environment, and a power supply portion (30) that applies alternating current (AC) voltage to the sensor portion. The sensor portion is structured to have impedance that is higher than that of sensor portion of a conventional environment sensor. The sensor portion has a dielectric disposed between first and second electrode plates (11,13) so that electrostatic capacitance between first and second electrode plates changes in accordance with specific physical quantity.    USE - Environment sensor e.g. humidity sensor applied to e.g. device having fixed power supplies for detecting humidity in air surrounding measurement environment. Can also be used in detecting temperature, pressure, radiation temperature, luminosity, airflow, vibration, inclination, position, ambient gas, dust, or the like. Can also be used in devices that are supplied with power from mobile power supplies or batteries, energy harvesting devices (environmental electrical power generators) that generate their own electricity through weak energy such as solar power electric generation, temperature differential electric generation, vibrational electric generation, bioelectric generation, airflow or wind-power electric generation, hydropower electric generation, wave power electric generation, rotary electric generation, or the like, and also to devices that are provided with mobile fuel cells, and, in particular, to devices that perform wireless communications that are mobile or portable.    ADVANTAGE - Reduces the amount of power consumed in sensor portion when compared to that of conventional environment sensor since impedance in sensor portion to which AC voltage is applied is higher than that of conventional environment sensor, thus enables reduction in the overall amount of electrical power consumed in the environment sensor. Enables stable detection over an extended period of time by reducing the likelihood of delamination of the dielectric and suppressing the reduction of sensitivity caused by swelling of dielectric. Enables increase in the detection sensitivity of electrostatic capacitance when the surface of first electrode plate has been set so as to be small, based on impedance of the sensor portion.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of a humidity sensor as an example of an environment sensor.    Sensor portion (10)    First and second electrode plates (11,13)    Humidity-sensitive film (12)    Power supply portion (30)    Humidity sensor (100)