A light source apparatus capable of controlling a quantity of light in a stable manner and an endoscope apparatus including the light source apparatus are provided. The light source apparatus includes a light source and a light quantity adjusting portion for limiting the light flux from the light source using an aperture blade. The light quantity adjusting portion includes the aperture blade which is driven to rotate in a vertical plane about a pivot and has a center of gravity which is decentered from the pivot, a position detecting portion for detecting a position of the aperture blade, a driving portion, and a light source controlling portion for controlling the driving portion. The light source controlling portion controls the driving portion based on the position of the aperture blade and a rotation direction.