PURPOSE: To simply reduce nonlineality of the output signal of a transmitter, by using a coefficient determined by specific spectrum component of a beat signal and incidental variation of a control signal, as a load coefficient, and updating it.

CONSTITUTION: Digital data processing arrangement 44 constituted of a microcomputer writes multiplication efficient nominal values α, β, γ, δ in a D/A converters 36-39, respectively, during initialization phase, and supplies them to multiplier 32-35. The values γ, δ a are 0, δ, and α, β are selected as the time constants of an integration circuit 18 and frequency to control voltage characteristics of a voltage controlled radio frequency oscillator, and give the starting frequency and the ending frequency necessary for the 1ms frequency sweep generated in the output of an oscillator 1, during the final 990ms of, e.g. each second, via a voltage adding circuit 31, according to reset signals applied to circuits 18-20. The value written in one out of the converters 36-39 is maintained until it is updated.