A digital AGC control method comprising: a first step in which an AGC unit outputs a setting value in accordance with a reference input value; a second step in which a control unit calculates an operation amount of a controlled object using the setting value; a third step in which an output unit generates an output signal representing the operation amount and outputs it to the controlled object; a fourth step in which a measuring unit calculates an operation measurement value of the controlled object; and a fifth step in which the measured value is input to the AGC unit, said first step including: a sixth step in which the AGC unit stores the reference input value in a first register (a), stores the measured value input in the fifth step in a second register (b), and calculates and stores in a third register (c) a deviation (e) between the reference input value stored in the first register (a) and the measured value; a seventh step in which a number of consecutive bits, other than a sign bit, of "0" value among higher-order bits in the first register (a) is detected; and an eighth step in which the deviation (e) stored in the third register (c) is shifted left by a number of bits in accordance with the number of bits detected in the seventh step to generate a deviation setting value as the setting value, wherein in the eighth step the number of bits shifted is the same as the number of bits detected. a first step in which an AGC unit outputs a setting value in accordance with a reference input value; a second step in which a control unit calculates an operation amount of a controlled object using the setting value; a third step in which an output unit generates an output signal representing the operation amount and outputs it to the controlled object; a fourth step in which a measuring unit calculates an operation measurement value of the controlled object; and a fifth step in which the measured value is input to the AGC unit, said first step including: a sixth step in which the AGC unit stores the reference input value in a first register (a), stores the measured value input in the fifth step in a second register (b), and calculates and stores in a third register (c) a deviation (e) between the reference input value stored in the first register (a) and the measured value; a seventh step in which a number of consecutive bits, other than a sign bit, of "0" value among higher-order bits in the first register (a) is detected; and an eighth step in which the deviation (e) stored in the third register (c) is shifted left by a number of bits in accordance with the number of bits detected in the seventh step to generate a deviation setting value as the setting value, wherein in the eighth step the number of bits shifted is the same as the number of bits detected. a sixth step in which the AGC unit stores the reference input value in a first register (a), stores the measured value input in the fifth step in a second register (b), and calculates and stores in a third register (c) a deviation (e) between the reference input value stored in the first register (a) and the measured value; a seventh step in which a number of consecutive bits, other than a sign bit, of "0" value among higher-order bits in the first register (a) is detected; and an eighth step in which the deviation (e) stored in the third register (c) is shifted left by a number of bits in accordance with the number of bits detected in the seventh step to generate a deviation setting value as the setting value, wherein in the eighth step the number of bits shifted is the same as the number of bits detected.