A pi /2 phase shifter generates first and second signals (SIGa, SIGb) of equal amplitude and different phases and first and second inverted signals (/SIGa, /SIGb) whose phases are opposite to those of the first and second signals, depending on an input signal. A first output signal (SIGOa) is produced by the addition of the first signal (SIGa) and the second signal (SIGb), and a second output signal (SIGOb) is produced by the addition of the first signal (SIGa) and the second inverted signal (/SIGb). The first output signal (SIGOa) and the second output signal (SIGOb) correspond to the diagonals of a rhombus formed of a vector (v3) indicating the first signal and a vector (v4) indicating the second signal, respectively, since the first and second signals (SIGa, SIGb) have the same amplitude. Consequently, the phase difference between the first and second output signals from the pi /2 phase shifter is set accurately at pi /2 irrespective of whether the phase difference between the first and second signals is pi /2.