An endoscope reduces a diameter of an insertion portion, and cleanses an observation optical system with a guide wire being inserted. The endoscope includes: an elongated insertion portion to be inserted into a body cavity an observation optical system at a distal end of the insertion portion to collect light from a subject a channel portion formed in a longitudinal direction of the insertion portion, through which a fluid is passed and a guide wire is inserted a seal portion in the channel portion to seal a gap between the channel portion and the guide wire where the guide wire is inserted through the channel portion and an opening portion on a proximal end side of the seal portion to discharge a fluid flowing through the channel portion toward the observation optical system.
