PURPOSE: To simplify the configuration of a revolving position sensing device and enhance the durability of the device when the relative positioning of an upper revolving body with a lower running body is to be checked.

CONSTITUTION: On the undersurface of an upper revolving body 14, a plurality of position sensors 17, 18 are installed in proximity to the surface. When the upper revolving body 14 rotates and the sensors 17, 18 reach over a left and a right crawler 12a, 12b, the switches of these sensors 17, 18 are changed over one after another. From the switching conditions of the sensors 17, 18, a control part 20 senses the revolving position of the upper revolving body 14.