PURPOSE: To improve the efficiency of selective operation by preventing trouble, in which the resetting operation of an operation attitude is required at every attitude changeover operation of a control tower and instantaneously resetting the operation attitude selected once correctly even when the operation attitude selected once is worked to a getting-on-and-off attitude.

CONSTITUTION: In a backhoe brought to a movable state at an operation attitude projecting to a getting-on-and-off path S and a getting-on-and-off attitude retreating from the path S regarding a control tower 15 with a control lever 13, a lock piece 24 on the machine body side, a single notch 23a for setting the getting-on-and-off attitude installed to the lock plate 17 of the control tower 15 and a plurality of notches 23 for setting the operation attitude are arranged. A selecting member 28 selecting the notch engaged with the lock piece 24 only at one position and a selecting operation mechanism Q capable of fixing and releasing the selecting member 28 at a selected position are mounted to the lock plate 17. The control tower 15 is reproduced at a set operation attitude.