An apparatus for controlling a laser device comprises means for outputting at least two levels of reference voltage from which a reference voltage is selected in accordance with the consecutive excited time of a laser rod which is excited to emit laser light by a light source. The light source is turned on under a charged voltage of capacitance th level of which is controlled in comparison with the reference voltage so that the laser light is precisely controlled in its energy density and radiation angle to avoid the influence of thermal lens effect of the laser element. This is accomplished by selecting an appropriate level of the reference voltage from the two or more levels of reference voltage.