Abstract: An objective of the present invention is to provide a friction stir welding device with which the temperature in the proximity of a weld part on a member to be welded can be intermittently measured by enabling the temperature of a plurality of sites in a rotary tool (4) used for friction stir welding to be ascertained in real-time when welding. This rotary tool (4) for a friction stir welding device comprises: a hollow channel (26a) that extends from the upper end of a shoulder part (4c) to the proximity of the lower end of a probe (4d), and that is on substantially the same axis as the axis of rotation of the shoulder part (4c); and a hollow, outer periphery channel (26b) that is apart from the axis of rotation of the shoulder part (4c) in the radial direction and in proximity of the outer periphery of the shoulder part (4c), and that extends from the upper end of the shoulder part to the proximity of the lower end thereof.

Abstract: In order to evaluate the cooling performance of cutting oil, cooling water, and the like more accurately than conventional means, there are provided a temperature measurement method and a temperature measurement device that can actually ascertain the temperature of a rotating tool such as a cutting tool during cutting or welding torch during welding in real time. The temperature measurement method uses a rotating holder that is rotatable around a rotating axis and has a hollow hole extending from a front end to a rear end along the rotating axis, and a rotating tool that is connected to the rotating holder and has a coaxial through hole with the hollow hole.