What is claimed is a compound represented by the following structural formula:or a pharmaceutically acceptable salt, solvate or clathrate thereof. The apparatus includes a detecting circuit configured to detect inflow current flowing from the image carrier into the forward bias applying circuit, and a decision circuit configured to determine a lower limit of the reverse bias voltage based on a detected value of the inflow current when the detected value of the inflow current exceeds a first predetermined value. The movable foot support is adapted to be engaged by the user’s feet to absorb the energy of movement in a first direction and to provide the user with a bouncing movement, which the user may translate into a movement of the movable body support in the opposite direction.