Provided is a light source device including a fiber laser, an amplifier, and a nonlinear fiber. Group delay dispersions D1 and D2 are a positive value, the light velocity in a vacuum is denoted as c, a spectral full width at half maximum of the pulse light is denoted as Δλ, the center wavelength of the pulse light is denoted as λ, a coefficient based on a shape of the pulse light is denoted as a, a value of the spectral full width at half maximum Δλ at which a function T(Δλ): T ⁡ ( Δλ ) = ( a × λ 2 c × Δλ ) ⁢ 1 + [ ( D ⁢ ⁢ 1 + D ⁢ ⁢ 2 ) ⁢ ( c × Δλ a × λ 2 ) 2 ] 2 is the minimum is denoted as Δλ_min, and Δλ at which a change amount of T(Δλ) when Δλ increases by 1 nm of λ becomes −3 dB is denoted as Δλ_3 dB, and Δλ satisfies Δλ_3 dB≤Δλ≤Δλ_min×2.