PURPOSE: To make easier the operability of a power shovel by a method in which a model link mechanism provided with proportionally contracted front mechanism for a power shovel is provided, and control is performed such that the deviation of relative angle between the front mechanism and the model link mechanism is zeroed.

CONSTITUTION: A boom 2 is pivotally supported in a vertically rocking manner on the upper slewing base 1 of a mobile body, an arm 3 is pivotally supported on the tip of the boom 2, and a bucket 4 is pivotally supported on the tip of the arm 3. At each pivotal point, a potentiometer is provided. A model link mechanism consisting of portions 2', 3', and 4' contracted similarly to the boom, arm, and bucket of the power shovel and the potentiometers of each pivotal point is also provided. A feedback control is made such that the deviation between the detection signal of the potentiometer of the power shovel and the detection signal of the model link mechanism is zeroed. The operation of the power slovel can thus be made easier.