An optical amplifying apparatus, comprising: a plurality of optical amplifying means for amplifying a plurality of optical signals, each of the plurality of optical amplifying means including a gain medium; a plurality of laser light generating means for generating a plurality of laser beams; at least one optical coupling means for coupling the plurality of laser beams variably in accordance with a coupling factor and outputting a plurality of excitation light beams, each of the plurality of excitation light beams exciting the gain medium; power monitoring means for monitoring an output level of optical signal having passed through each of the plurality of gain mediums; and controlling means for controlling the coupling factor and an output power of each of the plurality of laser light generating means, wherein the controlling means is configured, when a power limit of one of the plurality of laser light generating means is reached, to control each output power of the plurality of laser light generating means to minimize the power consumption of the plurality of laser light generating means, and to adjust the coupling factor of the optical coupling means wherein the controlling means is configured to calculate a ratio of the output level to a target value of non-null for auto power control, evaluate efficiency for generating each of the plurality of laser beams, decrease optical power of laser beam with the efficiency lowest among the plurality of laser beams when the output level being greater than the target value, and increase optical power of laser beam with the efficiency highest among the plurality of laser beams when the output level being smaller than the target value. a plurality of optical amplifying means for amplifying a plurality of optical signals, each of the plurality of optical amplifying means including a gain medium; a plurality of laser light generating means for generating a plurality of laser beams; at least one optical coupling means for coupling the plurality of laser beams variably in accordance with a coupling factor and outputting a plurality of excitation light beams, each of the plurality of excitation light beams exciting the gain medium; power monitoring means for monitoring an output level of optical signal having passed through each of the plurality of gain mediums; and controlling means for controlling the coupling factor and an output power of each of the plurality of laser light generating means, wherein the controlling means is configured, when a power limit of one of the plurality of laser light generating means is reached, to control each output power of the plurality of laser light generating means to minimize the power consumption of the plurality of laser light generating means, and to adjust the coupling factor of the optical coupling means wherein the controlling means is configured to calculate a ratio of the output level to a target value of non-null for auto power control, evaluate efficiency for generating each of the plurality of laser beams, decrease optical power of laser beam with the efficiency lowest among the plurality of laser beams when the output level being greater than the target value, and increase optical power of laser beam with the efficiency highest among the plurality of laser beams when the output level being smaller than the target value. calculate a ratio of the output level to a target value of non-null for auto power control, evaluate efficiency for generating each of the plurality of laser beams, decrease optical power of laser beam with the efficiency lowest among the plurality of laser beams when the output level being greater than the target value, and increase optical power of laser beam with the efficiency highest among the plurality of laser beams when the output level being smaller than the target value.