Light source device, comprising: a discharge lamp (Ld) having a main discharge vessel (Bd) which is filled with a discharge medium, and having a pair of opposed main discharge electrodes (E1, E2), one of the main discharge electrodes being held in a first electrode sealing part of the main discharge vessel at one end of the main discharge vessel and the other of the main discharge electrodes being held in a second electrode sealing part of the main discharge vessel at an opposite end of the main discharge vessel (Bd), a reflector which reflects radiant light from the discharge lamp (Ld) by means of a reflection film which has been formed on an inner side of the reflector, light being reflected in a direction toward a light exit window formed at a front end of the reflector, and a starting electrode (Wt) located in the outside peripheral area of the main discharge vessel (Bd), an auxiliary light source (Lx) which has an auxiliary discharge vessel (Bx) which is filled with a discharge medium, a first outside electrode (Eu) on an outer side of the auxiliary discharge vessel (Bx) and electrically connected to the starting electrode (Wt), said auxiliary light source (Lx) being mounted in one of the following ways without contact with the main discharge vessel (Bd), such that UV radiation which has been emitted from the auxiliary light source (Lx) can reach the main discharge vessel: - the auxiliary light source (Lx) is held by the reflector; - the auxiliary light source (Lx) is held by and in a base, the base being different from the reflector, the base being installed in a neck area of the reflector. a discharge lamp (Ld) having a main discharge vessel (Bd) which is filled with a discharge medium, and having a pair of opposed main discharge electrodes (E1, E2), one of the main discharge electrodes being held in a first electrode sealing part of the main discharge vessel at one end of the main discharge vessel and the other of the main discharge electrodes being held in a second electrode sealing part of the main discharge vessel at an opposite end of the main discharge vessel (Bd), a reflector which reflects radiant light from the discharge lamp (Ld) by means of a reflection film which has been formed on an inner side of the reflector, light being reflected in a direction toward a light exit window formed at a front end of the reflector, and a starting electrode (Wt) located in the outside peripheral area of the main discharge vessel (Bd), an auxiliary light source (Lx) which has an auxiliary discharge vessel (Bx) which is filled with a discharge medium, a first outside electrode (Eu) on an outer side of the auxiliary discharge vessel (Bx) and electrically connected to the starting electrode (Wt), said auxiliary light source (Lx) being mounted in one of the following ways without contact with the main discharge vessel (Bd), such that UV radiation which has been emitted from the auxiliary light source (Lx) can reach the main discharge vessel: - the auxiliary light source (Lx) is held by the reflector; - the auxiliary light source (Lx) is held by and in a base, the base being different from the reflector, the base being installed in a neck area of the reflector. - the auxiliary light source (Lx) is held by the reflector; - the auxiliary light source (Lx) is held by and in a base, the base being different from the reflector, the base being installed in a neck area of the reflector.