Ultrasound observation apparatus 1 includes a main power button 4 for operating the on-off of the internal power supply unit 11 by the pressing, substantially parallel movable with the pressing direction of the main power button 4 in conjunction with the pressing of the main power button 4 Na and the moving member 22, provided in the power source unit 11 so as to contact with the moving member 22, and a built-in power switch 11a for switching on and off of the power source unit 11 by being pushed by the movement of the moving member 22, the main at the time of pressing the power button 4, to move more than a predetermined amount of movement d of the main power button 4, as the amount of movement of the contact portion of the built-in power supply switch 11a becomes smaller of the moving member 22, the contact portion It has a moving amount adjusting mechanism for adjusting the amount of movement,超音波観測装置1は、押圧により内部の電源ユニット11のオン・オフを操作する主電源ボタン4と、主電源ボタン4の押圧に連動して主電源ボタン4の押圧方向とほぼ平行に移動可能な移動部材22と、移動部材22と当接するように電源ユニット11に設けられ、移動部材22の移動に伴って押圧されることにより電源ユニット11のオン・オフを切り替える内蔵電源スイッチ11aと、主電源ボタン4の押圧時に、主電源ボタン4の所定の移動量dを超える移動に対して、移動部材22の内蔵電源スイッチ11aとの当接部分の移動量が小さくなるように、当接部分の移動量を調整する移動量調整機構と、を有する。
