Light Source Device and Projector

A light source device comprising:

• an arc tube that has a light emission portion containing a pair of electrodes;
• a cooling channel that has a downstream part branched into a first channel and a second channel, and configured to guide air toward the light emission portion via the first channel or the second channel;
• a rotational member disposed within the cooling channel in such a condition as to be rotatable around a predetermined rotation shaft by gravity, and configured to switch the cooling channel to the first channel when the light source device is set in a first position, and to the second channel when the light source device is set in a second position different from the first position, wherein
• a position of the center of gravity of the rotational member is located at a position shifted from the center between the rotation shaft and an end of the rotational member away from the rotation shaft toward the end.