An image forming apparatus comprising: a stepping motor; motor driving means (12, 13) for supplying a current to said stepping motor for driving said stepping motor, detecting means (13, 1311) for detecting a voltage corresponding to a current supplied to said stepping motor when said motor driving means supplies the current up to a first current value to said stepping motor; storing means for storing a threshold used for performing, based on a change of said voltage, determination of a relationship between a load torque required for driving said stepping motor and an output of said stepping motor to be driven with said first current value; setting means for changing said first current value to a second current value calculated as a result of performing said determination using said threshold; and charcaterized by determining means (1312, 1313, 1315) for performing said determination, which includes: inflection point detecting means for detecting an inflection point from a rising area of a voltage waveform by using a voltage value detected in said detecting means; and means (1313, 1315) for determining, by comparing a position of said inflection point in the rising area of said voltage waveform with an aim position being said threshold, whether an output of said stepping motor driven by said first current value is excessive for the load torque required for driving said stepping motor. a stepping motor; motor driving means (12, 13) for supplying a current to said stepping motor for driving said stepping motor, detecting means (13, 1311) for detecting a voltage corresponding to a current supplied to said stepping motor when said motor driving means supplies the current up to a first current value to said stepping motor; storing means for storing a threshold used for performing, based on a change of said voltage, determination of a relationship between a load torque required for driving said stepping motor and an output of said stepping motor to be driven with said first current value; setting means for changing said first current value to a second current value calculated as a result of performing said determination using said threshold; and charcaterized by determining means (1312, 1313, 1315) for performing said determination, which includes: inflection point detecting means for detecting an inflection point from a rising area of a voltage waveform by using a voltage value detected in said detecting means; and means (1313, 1315) for determining, by comparing a position of said inflection point in the rising area of said voltage waveform with an aim position being said threshold, whether an output of said stepping motor driven by said first current value is excessive for the load torque required for driving said stepping motor. inflection point detecting means for detecting an inflection point from a rising area of a voltage waveform by using a voltage value detected in said detecting means; and means (1313, 1315) for determining, by comparing a position of said inflection point in the rising area of said voltage waveform with an aim position being said threshold, whether an output of said stepping motor driven by said first current value is excessive for the load torque required for driving said stepping motor.