To provide an illuminating device, an illuminating device for imaging, and an imaging system, which are able to optically increase a range where a light distribution angle (emission range) can be altered, compared to a conventional one, without making the device configuration complex and large.

In order to solve the problem, an illuminating device 10 or a projection device 101 for imaging, according to the invention, comprises a light source 11, and an optical lens part 13 having a specific refractive power, and emits light from the light source 11 via the optical lens part 13. In the illuminating device 10 or the projection device 101 for imaging, a convertible lens part 12 able to vary a focal position with the lens position fixed is provided between the light source 11 and the optical lens part 13. Light emitted from the light source 11 is made incident on the optical lens part 13 via the convertible lens part 12.