A wavelength conversion device comprising: a nonlinear medium, functioning as gain medium, including quantum dots; a first optical system for injecting a signal light having a wavelength to the nonlinear medium; a tunable laser having a tunable oscillation wavelength; a second optical system for injecting a laser light formed by the tunable laser to the nonlinear medium; and a tunable filter for selectively extracting output light generated from optical four wave mixing in the nonlinear medium, the tunable filter having a tunable frequency at which it extracts the output light, wherein the gain medium includes a semiconductor substrate and an active layer formed on the semiconductor substrate, wherein the quantum dots are formed in an island-like manner in the active layer by a material for forming strain with respect to the semiconductor substrate, and are covered by a barrier layer for lattice matching with respect to the semiconductor substrate, the first optical system includes a first optical amplifier for amplifying the signal light with a first amplification factor (α), the second optical system includes a second optical amplifier for amplifying the laser light with a second amplification factor (β), the wavelength conversion device further including a control apparatus for controlling the first and second optical amplifiers (41, 43), the control apparatus altering the first and second amplification factors (α, β) based on the absolute value of the difference (Δf) between the wavelength of the signal light and a wavelength of the laser light, wherein the control apparatus is configured to compensate for the decrease of the output light power associated with the increase in the difference (Δf). a nonlinear medium, functioning as gain medium, including quantum dots; a first optical system for injecting a signal light having a wavelength to the nonlinear medium; a tunable laser having a tunable oscillation wavelength; a second optical system for injecting a laser light formed by the tunable laser to the nonlinear medium; and a tunable filter for selectively extracting output light generated from optical four wave mixing in the nonlinear medium, the tunable filter having a tunable frequency at which it extracts the output light, wherein the gain medium includes a semiconductor substrate and an active layer formed on the semiconductor substrate, wherein the quantum dots are formed in an island-like manner in the active layer by a material for forming strain with respect to the semiconductor substrate, and are covered by a barrier layer for lattice matching with respect to the semiconductor substrate, the first optical system includes a first optical amplifier for amplifying the signal light with a first amplification factor (α), the second optical system includes a second optical amplifier for amplifying the laser light with a second amplification factor (β), the wavelength conversion device further including a control apparatus for controlling the first and second optical amplifiers (41, 43), the control apparatus altering the first and second amplification factors (α, β) based on the absolute value of the difference (Δf) between the wavelength of the signal light and a wavelength of the laser light, wherein the control apparatus is configured to compensate for the decrease of the output light power associated with the increase in the difference (Δf).