PURPOSE: To minimize call interrupting time by controlling a press signal by estimating the rise and fall characteristics of a radio set.

CONSTITUTION: After detecting an interrupt reception date request signal (a), a call station is controlled so as to turn off switches 40 and 42 at the point t3 delayed by a prescribed time. Namely, call is prevented from being interrupted by setting the delay time consistently with the rising characteristic (e) of an interrupting station radio transmitter. At the time t4 preceeded by a prescribed period from the point t1 of the time when a switch 2 is turned off, the switches 40 and 42 are turned on. Namely, the call station radio transmitter does not rise (c) up to the point t4, so that the interrupt time at the call station is reduced from t3 to T1.