PURPOSE: To reduce an error caused by waveform shaping by bringing a radiation pulse signal to A/D conversion, delaying and attenuating the obtained digital signal, calculating a complement and adding the digital signal which is subjected to complement processing and the original digital signal.

CONSTITUTION: A radiation pulse signal (a) is outputted as a sampling pulse (b) through a high speed discriminator 11, brought to A/D conversion 13, and outputted as a digital signal (c). This signal (c) is sent to a digital adding circuit 14, and also, sent to a digital delaying circuit 15, and inputted to an attenuating and complement calculating circuit 16 after a prescribed delay time is given. A digital signal (d) which is delayed, attenuated and brought to complement processing in such a way is added 14 to the original signal (c), and its output signal (e) is cut as to its latter half part, and becomes that which is shortened. This signal (e) is sent to a digital adder 17 and integrated by being added one after another in accordance with an integral timing pulse which is sent from a pulse generating circuit 12. In such a way, the adjustment is simplified, and an error caused by waveform shaping can be reduced.