Intended is to provide a strainer having a switch mechanism, which is hardly rattled by a wear, which can be stably operated by a weak force, which does not load a snare assembly and which can maintain an excellent operation feel, and a snare assembly holding structure which has a reliable clamping force so that it can prevent the looseness of the snare assembly end portion. An operation lever is hinged on its base end side to a base body. A link is turnably connected on its one end side to the lower side portion of a snare assembly holding member, and is likewise turnably connected on its other end side to a midway position of the operation lever. When the operation lever turns upward, the snare assembly holding member is pulled upward through the link. When the operation lever turns downward, the snare assembly holding member is pushed downward.