PURPOSE: To shorten the processing time by inputting timing signals shifted from one another by one clock based on the clock signal of a 4-multiplied carrier to perform specific switching operation.

CONSTITUTION: In a modulator D for communication machine, a generator 1 which generates a clock (a) having the 4-multiplied carrier signal frequency, a counter and decoder 2 which generates timing signals (b), (c), (d), and (e) of one clock period which are shifted from one another by one clock based on the signal (a), and a circuit 3 which takes signals (b) to (e) and other signals I and Q as the input to perform the switching operation are combined to repeatedly output the signal I, the signal the inverse of Q, the signal the inverse of I, and the signal Q in order. Consequently, an amplitude modulation signal is outputted without using multipliers neither adders. Thus, the purpose is attained in the simple circuit constitution, and the processing time is shortened, and further, the production cost and the space are reduced, and examination is simplified.