In a light source unit (210) serving as an embodiment of an illuminating apparatus, when P is a light-emitting element pitch [mm], and H is an optical axis distance [mm] between light-emitting elements (212) and an original (G), and when, in an illuminance cycle (T) representing repetition of bright and dark areas in a main scanning direction (X) on a light-irradiated face (Gs) of the original (G) caused by the light-emitting elements (212), the light-emitting element pitch (P) and the optical axis distance (H) are set such that unevenness [%] (M) (=(L1−L2)/L3 [%]) obtained by dividing a value obtained by subtracting a minimum illuminance value (L2) from a maximum illuminance value (L1) by an average illuminance value (L3) and an inter-unevenness distance [mm] (N) which is a half cycle of the illuminance cycle (T) satisfy the relation M≦N/2−5.5, and more preferably, M≦N/2−7.5.