To provide an antenna mechanism for forming radiation patterns in two different directions nearly simultaneously, and a radar device using the antenna mechanism.

An antenna mechanism 1 is constituted so that transmission electronic waves that are alternately switched by a switcher 13 can be alternately supplied to a pair of primary radiators 12a and 12b that are arranged oppositely. A beam formation part 11 is formed nearly at the center of a pair of primary radiators 12a and 12b to form radiation beams at space by receiving transmission electronic waves from the primary radiators 12a and 12b. Therefore, beams can be formed nearly simultaneously in different directions by a switching operation for the transmission electronic waves, thus a beam scanning region can be expanded. As a result, a wide space can be scanned in the same scanning time with a simple configuration without adopting a rotary mechanism, an advantage is obtained, where a radar rate can be reduced to half with a simple configuration by adding a function for controlling a switcher 13 to the radar device when the antenna mechanism 1 is adopted as the antenna of the radar device.