A light source device includes a phosphor wheel, a light source, a color separating-and-mixing element, and a light-guide optics. The phosphor wheel includes a base plate having a first light passage area and a second light passage area as a pair of light passage areas being annularly and point symmetrically arranged with respect to a center of the base plate, a phosphor area annularly formed on the base plate, and a motor that rotates the base plate. The color separating-and-mixing element disposed between the light source and the phosphor wheel changes a direction of traveling of fluorescence created as a result of light having being incident on the phosphor area and been converted in wavelength. The light-guide optics is provided to cause light from the light source to travel through the first light passage area, then through the second light passage area, and finally enter into the color separating-and-mixing element.