A power source includes: a generator; a turbine device that drives and rotates the generator; and a control device that: monitors a rotation speed of the generator; calculates a first adjusting power instruction value corresponding to a deviation between a reference value and an observed value of the rotation speed of the generator; acquires an adjusting power amplification coefficient from an external device; calculates a second adjusting power instruction value indicating a degree of increase of the adjusting power, based on the first adjusting power instruction value and the adjusting power amplification coefficient; amplifies the adjusting power based on the second adjusting power instruction value; and outputs the amplified adjusting power to the turbine device to adjust power supply from the generator and reduces fluctuation of frequency in a power transmission and distribution system.