PURPOSE: To effectively perform space diversity synthesis in a broad incoming level range, by providing an automatic gain control amplifier for an input side of an infinite phase shifter and a variable attenuator for an output side, and controlling the gain of the automatic gain controlling amplifier at the variable attenuator.

CONSTITUTION: An amplifier 5 amplifies an input signal with automatic control and applies an output to a 90° hybrid 1. Thus, an infinite phase shifter consisting of a hybrid 1, double balanced mixers 2, 3, and an in-phase hybrid 4 is activated at a constant input level at all times, the characteristics of an output level to a control voltage are always constant and the phase rotation of the output can stably be done. A variable attenuator 6 applies an AGC control voltage of the amplifier 5 as the control signal by applying an AGC control voltage of the amplifier 5 as the control signal to produce the attenuation to cancell the gain of the amplifier 5. As a result, the level of an output signal passing through the output of the hybrid 4 to the attenuator 6 is made equal to the input of the amplifier 5 and the phase rotation can stably be done.