A medical device includes: an insertion portion formed in an elongated shape that can be inserted into an insertion hole of an insertion assisting instrument that assists insertion into a body cavity of a subject a light guiding member configured to guide a light supplied from a light source to a distal end portion of the insertion portion and an interlock mechanism provided in the insertion portion and configured to, in conjunction with an insertion state of the insertion portion with respect to the insertion hole, transition to either one of a state in which emission of a light to a front of the distal end portion of the insertion portion is possible and a state in which emission of a light to the front of the distal end portion of the insertion portion is not possible.
