An endoscope apparatus includes an endoscope insertion section and an optical adapter that is detachably attachable to the endoscope insertion section. In the optical adapter, an LED and a resistor for connection detection are connected in parallel to two electric contacts. In the endoscope insertion section, two signal lines are connected to electric contacts, which are connectable to the two electric contacts in the optical adapter. The endoscope apparatus includes an attachment-and-detachment determining power supply that is connected to one of the signal lines through a switching circuit, and an optical-adapter-attachment-and-detachment determining section. When connection of the optical adapter is detected, the switching circuit is switched to supply an electric current for turning on the LED from an LED turn-on power supply to the one of the signal lines.