Initial magnetic pole estimating apparatus for an AC synchronous motor equipped in an AC synchronous motor controller, which has a speed gain control unit, mode section determining means, first command torque calculating means for selecting a first or a second cyclic section in accordance with the result in the mode section determining means, and determining whether or not a command speed is in a data acquisition speed section when the first cyclic section is selected, and calculating first command torque data from a command torque in the data acquisition speed section, second command torque calculating means for determining whether or not the command speed is in the data acquisition speed section when the second cyclic section is selected, and calculating second command torque data from the command torque in the data acquisition speed section, and estimated initial magnetic pole calculating means for calculating an estimated initial magnetic pole position using information on the first command torque data and second command torque data.