target swivel angle u03b1 1 is calculated by substituting the vehicle velocity v and the steady circle turning radius r calculated at step s 51 to the following equation 2 note that in equation 2 t denotes the light distribution point determination time and for example it is set to three seconds in equation 2 as described above t u00d7 v denotes the length of an arc on which the vehicle 7 is running along a circle having the steady circle turning radius r at the velocity v for t seconds as shown in fig7 the center angle of the arc with the length t u00d7 v 2 in the circle having the steady circle turning radius r shall become the target swivel angle u03b1 1 accordingly the target swivel angle u03b1 can be calculated from equation 2 as described above in fig7 numeral 40 denotes the actual running line of the vehicle 7 if it is assumed that the vehicle 7 is running at the velocity v the vehicle 7 which is positioned at the current position x will be positioned substantially at a distribution point pct seconds later accordingly the target swivel angle u03b1 1 is to be set so that an optical axis li of each headlight 2 passes through the light distribution point pc thereof the sub routine shown in fig4 for calculating the target swivel angle u03b1 2 will now be described in.