To provide a quadrature modulation circuit which is suitable for miniaturization and for a semiconductor integrated circuit.

An output signal frequency of a signal generation circuit 4 is subjected to frequency division to 1/4 times by using a two-multiplication circuit 10 and 1/2 frequency dividing circuits 11 to 13, and two signals where the phase difference between them is defined as 90° are generated. They are multiplied as the in-phase component and orthogonal component of a carrier by 1st and 2nd baseband signals I and Q in two multiplication circuits 14 and 15. Two multiplication results are added by an adding means 18, the added result and its inverted result are given to a 90° phase shifting circuit to obtain phase shifted results where the phase difference between them is defined as 90° and results where their results are inverted. They are respectively multiplied by two signals which are outputs of the circuit 12 and mutually have 90° phase difference in multiplication circuits 16 and 17. An image frequency component is suppressed by adding outputs of the two circuits 16 and 17 in an addition circuit 19.