PURPOSE: To improve operating efficiency by installing a working machine rocked in the vertical direction by the expansion and contraction of a dump cylinder with a base-section cylinder chamber and a front-section rod-side cylinder chamber at the front end of a lift arm.

CONSTITUTION: When soil and sand, etc., are scooped up by a bucket 32, a changeover valve 62 for a dump cylinder is changed over and the nose rod 43 of the dump cylinder 41 is retreated, and the bucket 32 is scoop-operated and a top-face opening section 32b is held under the state, in which the opening section 32b runs approximately parallel with a ground surface 20. A changeover valve 61 for a derricking cylinder is changed over and a piston rod 31 is projected, and a lift arm 23 is elevated. The front-section rod 53 of an auxiliary cylinder 51 is projected, oil in a cylinder chamber 55 flows into the cylinder chamber 46 of a cylinder 41, and oil in the cylinder chamber 45 of the cylinder 41 flows into the cylinder chamber 56 of the cylinder 51. The rod 43 is projected, the bucket 32 is pushed by the cylinder 41 and rotated while using a pivotal shaft 33 as a fulcrum, and the opening section 32b is lifted under the state, in which the opening section is held under the state, in which the opening section runs parallel with the ground surface 20, thus preventing the falling of soil and sand, etc.