A fiber laser device comprising: a seed light source that includes a seed light generation pumping light source which is adapted to emit seed light generation pumping light, a seed light generation optical fiber on which the seed light generation pumping light is incident and to which an active element that is pumped by the seed light generation pumping light is added, and an optical switch which is optically coupled to the seed light generation optical fiber and is adapted to switch between a transmission state and a non-transmission state of light with a specific wavelength that is propagated through the seed light generation optical fiber, wherein a level of a pumped state of the active element in the seed light generation optical fiber is increased when the optical switch is in the non-transmission state and pulsed seed light with the specific wavelength is emitted when the optical switch is in the transmission state; an amplifier that includes an amplification pumping light source which is adapted to emit amplification pumping light and an amplification optical fiber on which the seed light and the amplification pumping light are incident and to which an active element that is pumped by the amplification pumping light is added, wherein the amplifier is adapted to amplify the seed light; and a control unit that is adapted to control the seed light source and the amplifier, wherein the control unit is adapted to instruct the amplification pumping light source to emit the amplification pumping light in a state in which the seed light generation pumping light is emitted from the seed light generation pumping light source and the optical switch is in the transmission state, wherein the control unit is adapted to change the optical switch from the transmission state to the non-transmission state, with the amplification pumping light being emitted from the amplification pumping light source, and change the optical switch to the transmission state again so that the seed light is emitted, wherein the control unit is adapted to perform control such that, as a desired pulse width of output light emitted from the amplifier is reduced, a period (T3;T4) for which the optical switch is in the non-transmission state becomes longer and the intensity of the amplification pumping light emitted from the amplification pumping light source is controlled such that the output light has a predetermined peak intensity, and wherein the control unit is adapted to control the amplification pumping light source such that, as the period (T3; T4) for which the optical switch is in the non-transmission state becomes shorter, the level of the pumped state of the active element in the amplification optical fiber when the seed light is incident on the amplification optical fiber increases. a seed light source that includes a seed light generation pumping light source which is adapted to emit seed light generation pumping light, a seed light generation optical fiber on which the seed light generation pumping light is incident and to which an active element that is pumped by the seed light generation pumping light is added, and an optical switch which is optically coupled to the seed light generation optical fiber and is adapted to switch between a transmission state and a non-transmission state of light with a specific wavelength that is propagated through the seed light generation optical fiber, wherein a level of a pumped state of the active element in the seed light generation optical fiber is increased when the optical switch is in the non-transmission state and pulsed seed light with the specific wavelength is emitted when the optical switch is in the transmission state; an amplifier that includes an amplification pumping light source which is adapted to emit amplification pumping light and an amplification optical fiber on which the seed light and the amplification pumping light are incident and to which an active element that is pumped by the amplification pumping light is added, wherein the amplifier is adapted to amplify the seed light; and a control unit that is adapted to control the seed light source and the amplifier, wherein the control unit is adapted to instruct the amplification pumping light source to emit the amplification pumping light in a state in which the seed light generation pumping light is emitted from the seed light generation pumping light source and the optical switch is in the transmission state, wherein the control unit is adapted to change the optical switch from the transmission state to the non-transmission state, with the amplification pumping light being emitted from the amplification pumping light source, and change the optical switch to the transmission state again so that the seed light is emitted, wherein the control unit is adapted to perform control such that, as a desired pulse width of output light emitted from the amplifier is reduced, a period (T3;T4) for which the optical switch is in the non-transmission state becomes longer and the intensity of the amplification pumping light emitted from the amplification pumping light source is controlled such that the output light has a predetermined peak intensity, and wherein the control unit is adapted to control the amplification pumping light source such that, as the period (T3; T4) for which the optical switch is in the non-transmission state becomes shorter, the level of the pumped state of the active element in the amplification optical fiber when the seed light is incident on the amplification optical fiber increases.