In Japan, the construction of extensive infrastructure such as roads, railways, airports, energy plants, and so on, became popular from the 1960s when the period of high economic growth began, and high-level investments continued for about 40 years. Recently, infrastructure serious accidents have occurred, which is caused by aging or lack of inspection are of significant social concern. Therefore, as the population declines in the future, infrastructure monitoring using wireless sensor networks (IoT, Internet of things) is an urgent issue. On the other hand, the power supply is indispensable for driving the sensor device and transferring data. In this research, focusing on microwaves (electromagnetic waves) radiated from broadcasting and/or telecommunication that have been rarely reused, a battery-less infrastructure monitoring sensor platform that uses electromagnetic waves as a power source is realized. The proposed system is composed of a circularly polarized wideband planar antenna, rectifier circuit with impedance matching circuit, sensor module and Bluetooth low energy (BLE) module. For the feasibility study, the temperature and humidity sensors are attached on the surface of a concrete block, which is the model of the infrastructure. The 920 MHz RF signal is injected into the receiving antenna as a power source. The data of the temperature and humidity are transmitted to the smartphone or laptop computer at every 2-s interval. We can obtain the battery-less infrastructure monitoring sensor platform.