A dimension measuring device for measurement of an outside diameter of a pin joint formed in the end portion of a pipe or tube, comprising: an end face following mechanism adapted to be butted against the end face of the pipe or tube in the longitudinal direction; a dimension measuring mechanism which is connected to the end face following mechanism to measure the outside diameter of the pin joint of the pipe or tube; and a pushingly moving mechanism for pushingly moving the end face following mechanism toward the end face in the longitudinal direction of the pipe or tube, wherein the end face following mechanism includes a plurality of three or more contact sensors (114a, 114b, 114c, 114d), which are arranged along one plane to detect a contact state, on the side where the end face following mechanism butts against the end face in the longitudinal direction of the pipe or tube, and is turnable around at least two axes (X, Y) intersecting at right angles with the direction normal to the plane and intersecting at right angles with each other; the pushingly moving mechanism is adapted to pushingly move the end face following mechanism into the state in which at least three contact sensors of the plurality of contact sensors (114a, 114b, 114c, 114d) detect that the end face following mechanism butts against the end face in the longitudinal direction of the pipe or tube; and the dimension measuring mechanism is pushingly movable integrally and is turnable integrally with the end face following mechanism, and adapted to measure the outside diameter of the pin joint of the pipe or tube when it is detected, by at least three contact sensors of the plurality of contact sensors (114a, 114b, 114c, 114d), that the end face following mechanism butts against the end face in the longitudinal direction of the pipe or tube. an end face following mechanism adapted to be butted against the end face of the pipe or tube in the longitudinal direction; a dimension measuring mechanism which is connected to the end face following mechanism to measure the outside diameter of the pin joint of the pipe or tube; and a pushingly moving mechanism for pushingly moving the end face following mechanism toward the end face in the longitudinal direction of the pipe or tube, wherein the end face following mechanism includes a plurality of three or more contact sensors (114a, 114b, 114c, 114d), which are arranged along one plane to detect a contact state, on the side where the end face following mechanism butts against the end face in the longitudinal direction of the pipe or tube, and is turnable around at least two axes (X, Y) intersecting at right angles with the direction normal to the plane and intersecting at right angles with each other; the pushingly moving mechanism is adapted to pushingly move the end face following mechanism into the state in which at least three contact sensors of the plurality of contact sensors (114a, 114b, 114c, 114d) detect that the end face following mechanism butts against the end face in the longitudinal direction of the pipe or tube; and the dimension measuring mechanism is pushingly movable integrally and is turnable integrally with the end face following mechanism, and adapted to measure the outside diameter of the pin joint of the pipe or tube when it is detected, by at least three contact sensors of the plurality of contact sensors (114a, 114b, 114c, 114d), that the end face following mechanism butts against the end face in the longitudinal direction of the pipe or tube.