A light source apparatus and a lighting device are provided. The light source apparatus includes a light source assembly, a power source assembly, a first end cap, and a second end cap. The light source assembly includes a light source part and a light diffuser. An interior of the light diffuser includes a first receiving space which extends along a lengthwise direction of the light diffuser and penetrates the light diffuser. The light source part is mounted in the first receiving space along a lengthwise direction of the light diffuser. The power source assembly includes a power source part and a power source cover. An interior of the power source cover includes a second receiving space which extends along a lengthwise direction of the power source cover and penetrates the power source cover. The power source part is mounted in the second receiving space.