A light-emitting device includes an optical fiber, a first light source unit, and a second light source unit. The optical fiber includes a wavelength converting portion. The wavelength converting portion is provided between a light incident portion and a light emerging portion. The wavelength converting portion contains a wavelength converting material. The wavelength converting material is excited by excitation light to produce a spontaneous emission of light having a longer wavelength than the excitation light and amplifies the spontaneous emission of light to produce an amplified spontaneous emission of light. The first light source unit makes the excitation light incident on the light incident portion. The second light source unit makes seed light, causing a stimulated emission of light to be produced from the wavelength converting material that has been excited by either the excitation light or the amplified spontaneous emission of light, incident on the light incident portion.