In order to prevent floating matters from attaching to a glass plate fixed on a leading end face of an endoscope insertion portion, gas-feed ports are formed around the glass plate. Between the glass plate and the gas-feed ports, a protective barrier is formed in a manner surrounding the glass plate. Ejection of gas through the gas-feed ports generates gas streams to remove unnecessary floating matters existing between the glass plate and an observation target from sight. The gas streams also generate secondary gas streams flowing toward the glass plate. Some of the secondary gas streams are drawn forward with the primary gas streams, while the other of the secondary gas streams collide with the protective barrier. The secondary gas streams cannot flow along the surface of the glass plate, which prevents floating matters flowing with the secondary gas streams from attaching to the surface of the glass plate.
