A wireless sensor device capable of constant operation without replacement of batteries. The wireless sensor device is equipped with a rechargeable battery and the battery is recharged wirelessly. Radio waves received at an antenna circuit are converted into electrical energy and stored in the battery. A sensor circuit operates with the electrical energy stored in the battery, and acquires information. Then, a signal containing the information acquired is converted into radio waves at the antenna circuit, whereby the information can be read out wirelessly.
