A light source unit for use with an endoscope. The light source including: a primary light source configured to emit primary light; and a first connector provided on an optical path of the primary light and to which each of a plurality of optical conversion units are attachable and removable. Wherein each of the plurality of the optical conversion units include an optical conversion element having an optical conversion function to convert optical properties of the primary light to generate secondary light and each of the plurality of the optical conversion units further having a second connector configured to detachably engage the first connector to transmit the primary light to the optical conversion element; and an optical conversion unit is selected from the plurality of optical conversion units based on the optical conversion function desired for the secondary light, the secondary light being an illumination light of the endoscope.