Abstract: In a vertical type heat exchanger including a water chamber delimited by a drum end plate and a header plate on which a large number of heat transfer tubes are arrayed, a novel manipulator for working in the heat exchanger is provided such that a support frame is disposed within the water chamber, a base end portion of a freely extensible and contractible main arm which is rotatable about its base end portion and vertically swingable about a fulcrum at its base end portion, is mounted on the support frame, a base end portion of a sub-arm which is rotatable about its base end portion and vertically swingable about a fulcrum at its base end portion and also which can be positioned in parallel to the header plate, is mounted at the tip end portion of the main arm, a vertically movable clamp shaft which can be inserted into the heat transfer tube is provided coaxially with the rotational axis of the sub-arm, and a position detector for detecting the position of the clamp shaft so as to assist in positioning the c