There is provided a vehicular lamp at low cost. A power source apparatus includes: an output controlling switch operable to intermittently carry an electric current; an output coil operable to accumulate energy according to the current flowing into the output controlling switch and to output an electric power based on the accumulated energy when the output controlling switch is turned off; an end detecting unit operable to detect that the output coil ends the output of the power; and an output controlling unit, in which the output controlling unit includes: a time memorizing unit that memorizes OFF time for which the output controlling switch should be kept off; a switch controlling unit that switches the output controlling switch on and off based on the OFF time memorized in the time memorizing unit; and a time changing unit that changes the OFF time memorized in the time memorizing unit. The time changing unit increases the OFF time when the end detecting unit is not detecting the end of the output and decreases the OFF time when the end detecting unit is detecting the end of the output, in the timing when the output controlling switch is turned on.