To correct the quantity of light in detail by reducing deviation of correction quantity.

A method for correcting the quantity of light reduces the difference in quantity of light between each light emitting element of an LED array 41, using light quantity correcting portions 100 and 110 to correct the quantity of light within a correction range. The correction range Es is set corresponding to the width of luminance distribution Bs of the light emitting element for each LED array, the correction range Es of the set range is commonly used between each LED array 41. The difference in quantity of light between each light emitting element is reduced by an LED array unit by correcting the quantity of light of the light emitting element of each LED array 41 by the light quantity correcting portion 110.