A light source apparatus comprising: a phosphor unit that emits fluorescent light by excitation caused by excitation light; an excitation light source unit that supplies said excitation light; a reflection unit that reflects said excitation light that is supplied from said excitation light source unit toward said phosphor unit and that transmits said fluorescent light that is emitted from said phosphor unit ; and collimator lens (15a-15c) that is provided between said reflection unit and said phosphor unit and whose focal distance differs according to wavelength; wherein: said phosphor unit is disposed at a position determined by the focal distance of said collimator lens (15a-15c) at the wavelength of said fluorescent light that is emitted from said phosphor unit ; and said collimator lens (15a-15c) includes at least one first lens having a negative power and at least one second lens having a positive power, the Abbe number of said second lens being smaller than that of said first lens; wherein the excitation light is condensed on said phosphor unit by means of said collimator lens (15a-15c) in a state that includes a certain defocus amount, whereby the optical energy density per unit area on said phosphor unit decreases and the damage to the phosphor can be mitigated. a phosphor unit that emits fluorescent light by excitation caused by excitation light; an excitation light source unit that supplies said excitation light; a reflection unit that reflects said excitation light that is supplied from said excitation light source unit toward said phosphor unit and that transmits said fluorescent light that is emitted from said phosphor unit ; and collimator lens (15a-15c) that is provided between said reflection unit and said phosphor unit and whose focal distance differs according to wavelength; wherein: said phosphor unit is disposed at a position determined by the focal distance of said collimator lens (15a-15c) at the wavelength of said fluorescent light that is emitted from said phosphor unit ; and said collimator lens (15a-15c) includes at least one first lens having a negative power and at least one second lens having a positive power, the Abbe number of said second lens being smaller than that of said first lens; wherein the excitation light is condensed on said phosphor unit by means of said collimator lens (15a-15c) in a state that includes a certain defocus amount, whereby the optical energy density per unit area on said phosphor unit decreases and the damage to the phosphor can be mitigated. said phosphor unit is disposed at a position determined by the focal distance of said collimator lens (15a-15c) at the wavelength of said fluorescent light that is emitted from said phosphor unit ; and said collimator lens (15a-15c) includes at least one first lens having a negative power and at least one second lens having a positive power, the Abbe number of said second lens being smaller than that of said first lens; wherein the excitation light is condensed on said phosphor unit by means of said collimator lens (15a-15c) in a state that includes a certain defocus amount, whereby the optical energy density per unit area on said phosphor unit decreases and the damage to the phosphor can be mitigated. <EOS>