PURPOSE: To easily carry out dug earth and sand by lowering a pair of triangular shells, setting the extending amount to a preliminarily calculated value and to simplify the operation of an excavating machine.

CONSTITUTION: A bucket B provided with a pair of triangular shells 6 which are opened and closed by elongation and contraction of a hydraulic cylinder 7 by making a pin 5 as a fulcrum and are set so that a width of an excavating surface at an expanding time may be larger than an outside diameter width at a closing time is mounted at a tip of a bar 3. This bar 3 is elevated and lowered within a longitudinal hole 2. After the shells 6 reach a prescribed depth, a cylinder 7 is driven, and the shells 6 are lowered, setting the expanding amount to a preliminarily calculated value.