A light source apparatus comprising: a light-emitting element; a temperature detector that detects a temperature of an installation location of the light-emitting element; a drive circuit that supplies a current to the light-emitting element; a control unit that controls the current supplied from the drive circuit to the light-emitting element; and a target light output receiving unit that receives an input of information corresponding to a target value Φ of a light output of the light-emitting element, wherein the control unit includes: a first storage unit in which a control function is stored, said control function is configured to obtain a third variable correlated with the current supplied to the light-emitting element from a first variable correlated with the temperature of the installation location of the light-emitting element and a second variable correlated with the light output of the light-emitting element; and an arithmetic processing unit that determines a supply current amount to the light-emitting element, which is the third variable, by reading the control function from the first storage unit, substituting a temperature T detected by the temperature detector for the first variable, and substituting the target value Φ for which the target light output receiving unit has received input for the second variable, wherein the drive circuit is configured to supply an amount of current corresponding to the supply current determined by the arithmetic processing unit to the light-emitting element; fl characterised in that the control function is a curved surface function specified in mathematical formula below that includes an independent variable x, an independent variable y, and a dependent variable z, the control function being a function converted into a formula for obtaining the third variable by assigning the first variable, the second variable, and the third variable to one of the independent variable x, the independent variable y, and the dependent variable z, and the curved surface function has a shape determined by a coefficient α ts, recorded in the first storage unit in the control unit, in mathematical formula below: z = ∑ t = 0 k ∑ s = 0 j α ts ⋅ y s ⋅ x t where α ts (0 ≤ t ≤ k, 0 ≤ s ≤ j) is the coefficient, one of k or j is an integer of 2 or more, and the other one of k or j is an integer of 1 or more. a light-emitting element; a temperature detector that detects a temperature of an installation location of the light-emitting element; a drive circuit that supplies a current to the light-emitting element; a control unit that controls the current supplied from the drive circuit to the light-emitting element; and a target light output receiving unit that receives an input of information corresponding to a target value Φ of a light output of the light-emitting element, wherein the control unit includes: a first storage unit in which a control function is stored, said control function is configured to obtain a third variable correlated with the current supplied to the light-emitting element from a first variable correlated with the temperature of the installation location of the light-emitting element and a second variable correlated with the light output of the light-emitting element; and an arithmetic processing unit that determines a supply current amount to the light-emitting element, which is the third variable, by reading the control function from the first storage unit, substituting a temperature T detected by the temperature detector for the first variable, and substituting the target value Φ for which the target light output receiving unit has received input for the second variable, a first storage unit in which a control function is stored, said control function is configured to obtain a third variable correlated with the current supplied to the light-emitting element from a first variable correlated with the temperature of the installation location of the light-emitting element and a second variable correlated with the light output of the light-emitting element; and an arithmetic processing unit that determines a supply current amount to the light-emitting element, which is the third variable, by reading the control function from the first storage unit, substituting a temperature T detected by the temperature detector for the first variable, and substituting the target value Φ for which the target light output receiving unit has received input for the second variable, the control function is a curved surface function specified in mathematical formula below that includes an independent variable x, an independent variable y, and a dependent variable z, the control function being a function converted into a formula for obtaining the third variable by assigning the first variable, the second variable, and the third variable to one of the independent variable x, the independent variable y, and the dependent variable z, and the curved surface function has a shape determined by a coefficient α ts, recorded in the first storage unit in the control unit, in mathematical formula below: z = ∑ t = 0 k ∑ s = 0 j α ts ⋅ y s ⋅ x t where α ts (0 ≤ t ≤ k, 0 ≤ s ≤ j) is the coefficient, one of k or j is an integer of 2 or more, and the other one of k or j is an integer of 1 or more.