PURPOSE: To keep a driver from a feeling of physical disorder for controlling a shade by changing a turning angle of the shade corresponding to the direction of the right or the left cornering (turning).

CONSTITUTION: When a motorcycle corners to the left side, a shade 9 is so turned that bright and darkness boundary lines 9a, 9b turn to the L direction, and corners to the right side, turn to the R direction. When the cornering is in a transient condition, a rapid variation of bank angle to be calculated is made to be suppressed as much as possible by multiplying a correction coefficient which is set as the larger bank angle, the less one, so that the calculation of the bank angle i.e., the control of the shade 9 can be accurately performed. With this constitution, it can keep a driver from a feeling of physical disorder for controlling the shade 9.