To prevent hydraulic oil feed pipes of both screw shafts from being connected with including grout remaining within a grout feed pipe when the preceding screw shaft and the following screw shaft are connected together after being separated from each other.

In this shaft joint of an excavating operation shaft, a male joint is provided at the upper end of the preceding excavating operation shaft; a female joint is provided at the lower end of the following excavating operation shaft; one type of used fluid supply passage and the other type of used fluid supply passage positioned inside one type of used fluid supply passage are each vertically and concentrically formed in both the excavating operation shafts; in the preceding excavating operation shaft, an upper end of the outside fluid supply passage is extended up to an upper end of the male joint; an upper end of the inside fluid supply passage is extended up to a position slightly lower than the upper end of the male joint; and an overflow port, which is in a position appropriately lower than the upper end of the inside fluid supply passage and which is opened to the outside fluid supply passage, is provided in an opened state on the outside surface of the male joint, and equipped with an opening/closing means which closes the overflow port by fitting the male joint into the female joint, and which opens the overflow port by disengaging the male joint from the female joint.