To prevent erroneous operation, operation stop, failure, and the like of various types of circuits even when excessive electrostatic noise is generated.SOLUTION: A patient circuit 203 comprises: a signal input terminal 211； a power supply terminal 212； an IC chip 213 that receives input of a signal from the signal input terminal 211 and executes signal processing； and a Y capacitor 214 connected between the patient circuit 203 and a secondary circuit 204. The secondary circuit 204 includes: a first area AR1 located farther than the patient circuit 203, as viewed from an endoscope 100； and a second area AR2 located closer than the patient circuit 203, as viewed from an endoscope 100. The Y capacitor 214 is connected between a secondary board SB 1 existing in the second area AR2 and a patient board SB1. A distance between the signal input terminal 211 and the Y capacitor 214 and a distance between the signal input terminal 211 and the power supply terminal 212 are shorter than a distance between the signal input terminal 211 and the IC chip 213.SELECTED DRAWING: Figure 1【課題】過大な静電気ノイズが発生した場合でも各種回路の誤動作、動作停止、故障などを防止する。【解決手段】患者回路２０３は、信号入力端子２１１と、電源端子２１２と、信号入力端子２１１から信号を入力されて信号処理を実行するＩＣチップ２１３と、患者回路２０３と二次回路２０４との間に接続されるＹコンデンサ２１４とを備える。二次回路２０４は、内視鏡１００から見て患者回路２０３よりも遠い位置にある第１領域ＡＲ１と、内視鏡１００から見て患者回路２０３よりも近い位置にある第２領域ＡＲ２とを有する。Ｙコンデンサ２１４は、第２領域ＡＲ２にある二次基板ＳＢ２と、患者基板ＳＢ１との間に接続される。信号入力端子２１１とＹコンデンサ２１４との間の距離、及び信号入力端子２１１と電源端子２１２との間の距離は、信号入力端子２１１とＩＣチップ２１３との間の距離よりも短い。【選択図】図１
