There are provided an illumination optical device and an endoscope that can suppress the temperature rise of a distal end portion of an endoscope.An illumination optical device is mounted in a distal end portion of an endoscope. The illumination optical device is adapted so that an optical rod, a first lens, a spacer ring, and a second lens are received on the inner periphery of a lens barrel in this order from the rear end side toward the distal end side. The lens barrel is made of metal and polishing is performed on the inner periphery of the lens barrel, so that reflectance is increased. Since reflectance on the inner periphery of the lens barrel is purposely increased in this way on the contrary to the related art, temperature rise can be suppressed. Further, since the illumination optical device has been designed in the related art on the premise that reflected light exists, design does not need to be significantly changed even in a case where reflectance is to be increased.
