the delay controller 198 delays the gain control signal and outputs the delayed gain control signal to the vga 150 as a result the gain of the vga 150 is changed with a delay to the change in the gain of the lna 120 s 70 13 if the gain of the lna 120 at the current point in time is the low gain at the step s 70 8 the change timing controller 196 does not output the delay control signal since the delay control signal is not output the delay controller 198 outputs the gain control signal to the vga 150 without delaying it as a result the gain of the vga 150 is changed simultaneously with a change in the gain of the lna 120 s 70 15 if the gain of the lna 120 does not pass through the threshold before and after the change at the step s 70 6 the delay control signal is not output the change timing controller 196 further makes a decision whether to change the gain of the vga 150 s 70 17 in this decision the gain comparator 201 previously stores a threshold located between the low gain and the high gain of the vga 150 and judges a gain higher than the threshold to be the high gain and judges gain lower than the threshold to be the low gain if the gain of the vga 150 passes through this threshold before and after the change the change timing controller 196 decides to change the gain of the vga 150 s 70 18 if the gain of the vga 150 is decided to be changed the gain control signal generator 192 outputs the gain.