An ultrasound observation apparatus 1 includes: a main power-supply button 4 that operates an internal power-supply unit 11 to be turned on/off as a result of depression of the main power-supply button 4； a moving member 22 capable of moving substantially in parallel to a direction of the depression of the main power-supply button 4 in conjunction with the depression of the main power-supply button 4； an internal power-supply switch 11 a provided at the power-supply unit 11 so as to be in contact with the moving member 22, the internal power-supply switch 11a switching the power-supply unit 11 on/off by being depressed along with movement of the moving member 22； and a movement amount adjusting mechanism that upon the depression of the main power-supply button 4, if an amount of movement of the main power-supply button 4 exceeds a predetermined movement amount d, adjusts an amount of movement of a contact portion of the moving member 22, the contact portion being in contact with the internal power-supply switch 11 a so that the amount of movement of the contact portion of the moving member 22 becomes smaller relative to the amount of movement of the main power-supply button 4.
