Abstract: A medical instrument whose distal end is inserted into a body cavity of a subject in cooperation with a treating unit, comprises an insertion section including a distal end inserted into the body cavity and having a first opening exposed there, a proximal base end located outside the body of the subject, and a channel provided in the insertion section and extending from the proximal base end toward the first opening, an operation section connected to the proximal base end and having a second opening leading to the channel, a mount piece provided around the second opening. A valve is provided on the mount piece including a body having a slit adapted to be opened when the treating unit is inserted into the channel and closed when it is withdrawn from the channel and an annular groove detachably fitted on the mount piece, and a thin-walled portion for destroying the valve when the valve is removed from the mount piece.

Abstract: A medical instrument whose distal end is inserted into a body cavity of a subject in cooperation with a treating unit, comprises an insertion section including a distal end inserted into the body cavity and having a first opening exposed there, a proximal base end located outside the body of the subject, and a channel provided in the insertion section and extending from the proximal base end toward the first opening, an operation section connected to the proximal base end and having a second opening leading to the channel, a mount piece provided around the second opening. A valve is provided on the mount piece including a body having a slit adapted to be opened when the treating unit is inserted into the channel and closed when it is withdrawn from the channel and an annular groove detachably fitted on the mount piece, and a thin-walled portion for destroying the valve when the valve is removed from the mount piece.