To provide a radar system which only requires establishment of one front end common to each antenna, without the need for setting up RF receiver circuit for each antenna.

In this radio system, a front end which time-division amplifies any sequentially-input signal received by each antenna, as well as frequency-converting it into an intermediate frequency signal, is provided commonly for each antenna. Each antenna is cyclically connected to the front end at a defined switching frequency, the intermediate frequency signal output from the front end is input to analog-to-digital (AD) converter provided for each antenna to be AD converted through an intermediate frequency filter, and then phase or amplitude of the signal output from each AD converter is adjusted into a composite signal, to detect an object from the desired direction.