A light source driving device, comprising: a storage unit configured to store therein three or more combinations of a brightness level indicating brightness of light emitted from a light source, and a control value used when light with brightness corresponding to the brightness level is emitted from the light source, each of the combinations including the brightness level and the control value corresponding to the brightness level, wherein there are nonlinear relationships between the control values and the brightness levels over the three or more sets of the combinations; and a control unit configured to receive a light control instruction signal and control the light source according to control values so that the brightness of the light emitted from the light source is gradually changed from an initial brightness level (Py) when the light control instruction signal is received during a first time period (t d) to a brightness corresponding to a target brightness level (Qy) indicated by the received light control instruction signal, characterized in that the control unit is further configured to calculate an intermediate brightness level (Ry, Rx') by interpolating the intermediate brightness level (Ry, Rx') between the initial brightness level (Py) when the light control instruction signal is received and the target brightness level (Qy), at each of a number of second time periods (α) that are shorter than the first time period (t d) and are comprised in the first time period (t d), and respectively calculate a control value (Ry') corresponding to the calculated intermediate brightness level (Ry, Rx') by using two (Px', Qx') of the stored brightness levels adjacent to the intermediate brightness level (Ry, Rx'), wherein the first time period (t d) is a time period in which the brightness of the emitted light is changed to the brightness corresponding to the target brightness level (Qy), the second time periods (α) are sequentially included in the first time period (t d), and the two (Px', Qx') of the stored brightness levels respectively include a brightness level (Px') greater than the intermediate brightness level (Ry, Rx') and a brightness level (Qx') smaller than the intermediate brightness level (Ry, Rx'). a storage unit configured to store therein three or more combinations of a brightness level indicating brightness of light emitted from a light source, and a control value used when light with brightness corresponding to the brightness level is emitted from the light source, each of the combinations including the brightness level and the control value corresponding to the brightness level, wherein there are nonlinear relationships between the control values and the brightness levels over the three or more sets of the combinations; and a control unit configured to receive a light control instruction signal and control the light source according to control values so that the brightness of the light emitted from the light source is gradually changed from an initial brightness level (Py) when the light control instruction signal is received during a first time period (t d) to a brightness corresponding to a target brightness level (Qy) indicated by the received light control instruction signal, characterized in that the control unit is further configured to calculate an intermediate brightness level (Ry, Rx') by interpolating the intermediate brightness level (Ry, Rx') between the initial brightness level (Py) when the light control instruction signal is received and the target brightness level (Qy), at each of a number of second time periods (α) that are shorter than the first time period (t d) and are comprised in the first time period (t d), and respectively calculate a control value (Ry') corresponding to the calculated intermediate brightness level (Ry, Rx') by using two (Px', Qx') of the stored brightness levels adjacent to the intermediate brightness level (Ry, Rx'), wherein the first time period (t d) is a time period in which the brightness of the emitted light is changed to the brightness corresponding to the target brightness level (Qy), the second time periods (α) are sequentially included in the first time period (t d), and the two (Px', Qx') of the stored brightness levels respectively include a brightness level (Px') greater than the intermediate brightness level (Ry, Rx') and a brightness level (Qx') smaller than the intermediate brightness level (Ry, Rx').