To provide an accurate crawling boring control without remarkably increasing cost.

When a shield machine bores at a normal speed, an oil introduction line 30 is connected to a main line 25 by a speed selector valve 29 to guide an oil of normal flow to the push side chamber 3 of a shield jack 1. When the shield machine bores at a very slow speed, the oil introduction line 30 is connected to a sub line 26 by the speed selector valve 29 to guide the oil restricted in flow by a restrictor 27 to the push side chamber 3 of the shield jack 1. The oil restricted in flow by the restrictor 27 is introduced into the push side chamber 3 of the shield jack 1 through a check valve 32 and an opening/closing valve 8 from which oil do not leak. Even if oil leakage occurs from the speed selector valve 29 and a push-pull selector valve 12, the shield jack 1 is extended at a speed (very slow speed) on which an oil flow restricted by the restrictor 27 is accurately reflected. Consequently, a shield machine body 15 can accurately bore at very slow speeds.