To provide a position sensorless controller of a motor which can achieve position sensorless control through a very simple processing (amount of operation).

The position sensorless controller of a motor comprises a section for superposing a superposition current having a frequency different from that of a motor drive current on the motor drive current, sections (31, 32) for extracting the γ-axis component iγ and the δ-axis component iδ of the superposition current from a motor current supplied to the motor, and control sections (35, 36) for controlling the motor (estimating the rotor position) such that the DC component ihD of the product of the extracted γ-axis component iγ and the δ-axis component iδ of the superposition current converges to zero.