To provide a light source unit capable of restraining the spread of a light beam emitted from a tapered rod to be much smaller, and an illumination device and a projector device.

The light source device is equipped with an LED 2 which irradiates a body to be irradiated 6 with the light beam, and the tapered rod 1 that is a tapered light guiding part arranged like the optical path of the light beam from the LED 2 to the body to be irradiated 6. The tapered rod 1 is constituted so that an end face on a side where the light beam from the LED 2 is emitted is made larger than an end face on a side where the light beam is made incident, and the end face on the emitting side is formed of a projecting shape surface such as a rounded surface.