A reflector has a reflection plane for reflecting light emitted from an LED light source in the direction that goes away from the optical axis of the LED light source with respect to the direction parallel to the optical axis, whereby the effective use of emitted light can be ensured by reflecting, for example, peripheral light, which normally cannot be effectively used, in a proper direction by the reflection plane and causing the reflected light to enter a diffusion lens. Further, by using the abovementioned reflection plane, the thickness of the reflector can be reduced and the diffusion effect of the emitted light can be increased, thereby enabling an increase in the flexibility of the design of the diffusion lens and a reduction in the thickness thereof, and consequently the thickness of an LED lighting device can be reduced.