the rising of the b light output and accordingly selects u201c 1 u201d on the other hand in other cases a result obtained by the division unit 63 dividing an output from the slowest signal selection unit 60 by c is outputted specifically in the case of fig4 since b is smallest an output from the switching unit 66 is b c furthermore an start up signal which is turned on only during a fixed period of time from start up is inputted to the switching unit 67 68 and 69 using a display start up signal as a trigger d the switching unit 67 selects an output from the switching unit 64 during the start up signal being on and otherwise selects u201c 1 u201d to stop adjustment specifically in the case of fig4 b a is outputted during a period during which the start up signal is on and u201c 1 u201d is outputted during other periods this serves as a light output adjustment value x e likewise the switching unit 68 selects an output from the switching unit 65 during the start up signal being on and otherwise selects u201c 1 u201d to stop adjustment specifically in the case of fig4 u201c 1 u201d is.