In a balanced modulator, a local oscillator frequency signal is transmitted through a serial connection of the primary side conductive patterns (1p and 2p) of a first coupler (1) and a second coupler (2), wherein the two couplers (1 and 2) are connected in an opposing direction. A first output terminal of the secondary side conductive pattern (1s) of the first coupler (1) is grounded through a first effective grounding pattern (4), and a first output terminal of the secondary side conductive pattern (2s) of the second coupler (2) is grounded through a second effective grounding pattern (5). The output voltage at a second output terminal of the secondary side conductive pattern (1s) of the first coupler (1) is impressed to a terminal of a first diode (9). The output voltage at a second output terminal of the secondary side conductive pattern (2s) of the second coupler (2) is impressed to a terminal of a second diode (10). A compensation pattern (3) is inserted between the serial connection of the primary side conductive patterns (1p and 2p) for compensating an unbalance caused by the two effective grounding patterns (4 and 5).