Depending on the setting energy attenuation, transmitting plate having a thickness has been adjusted (1) holder for holding transmitting plate (1) and (3), with a thickness of the transmissive plate (1) has been adjusted to a thickness corresponding to a predetermined ratio smaller attenuation than the set value together with the transmission plate (1) and holding portion on at least one of (3), the adjusting sheet is adjusted thickness smaller than the thickness corresponding to two times the amount of attenuation of a predetermined ratio (2), transmitting plate (1 superposition mechanism for detachably superposed are provided in).エネルギーの減衰量の設定値に応じて、厚みが調整された透過板(1)と、透過板(1)を保持する保持部(3)と、を備え、透過板(1)の厚みが、設定値よりも所定割合小さな減衰量に相当する厚みに調整されているとともに、透過板(1)および保持部(3)のうち少なくとも一方には、所定割合の2倍の減衰量に相当する厚み以下に厚みを調整された調整シート(2)を、透過板(1)に着脱自在に重畳させる重畳機構が設けられている。
