PURPOSE: To detect an object to be detected when it is inverted by piercing electrodes through one side of a box and bringing a conductor plate into contact by the weight of a granular load object.

CONSTITUTION: When a box 1 is laid with the fitting end side of electrodes 2, 3, with its bottom section facing upward, a granular load object 5 sealed in the box 1 is located on the top section opposite to the bottom section by the gravitational force. No load is thereby applied to a conductor plate 4 at the bottom section side, the protruded face 41 is protruded toward the top section, the electrodes 2, 3 are kept in the off state. On the contrary, when the electrode fitting end face side (bottom section) is turned downward from this state, the protruded face 41 is pushed to the electrodes 2, 3 side and brought into contact with end sections 21, 31 of the electrodes and set to the on state. The inversion state can be reliably detected accordingly.