A motor controller for controlling output of a motor by switching on and off switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2) arranged in a power supply line to said motor by control signals, comprising a current command value determination part (15, 50) for determining current command values corresponding to a target output of said motor; a calculation part (52, 56) for determining target applied voltage values to said motor corresponding to said current command values; a current determination part for determining values of current flowing in said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2); a calculation part for determining voltage command values by adding voltage drop values determined from the values corresponding to equivalent resistance and the values of current flowing in said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2) to said target applied voltage values; a signal generating part (18u, 18v, 18w, 54) for generating said control signals according to said voltage command values; and a voltage determination part for determining values of voltage applied to said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2), characterized in that an output of said motor being a three-phase brushless motor is open-loop controlled as the output of said motor via an inverter circuit constituted of said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2), U-phase current value, V-phase current value and W-phase current value, which are values of current flowing in the respective three-phase coils constituting an armature winding of said motor are determined as values of current flowing in said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2), said motor controller further comprises a rotation position determination part for determining rotation positions of a rotor (1 b) of said motor, a calculation part for calculating an angular velocity of said rotor based on said rotation positions, and a phase current coordinate conversion part for calculating a d-axis current value Id and a q-axis current value Iq based on said U-phase current value, said V-phase current value, said W-phase current value and said rotation positions, in which an axis along the magnetic flux direction of filed system of the rotor is taken as the d-axis, and an axis perpendicular to the d-axis and the rotation axis of the rotor is taken as the q-axis; and a storage part for storing relations between values corresponding to predetermined equivalent resistance which corresponds to power loss generated by switching on and off said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2), values of current flowing in said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2), and values of voltages applied to said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2), wherein said current command value determination part (15, 50) has a dq-axes current command value calculation part for determining a d-axis current command value and a q-axis current command value as said current command values based on the target output of said motor, said voltage determination part has a voltage detector which detects actual voltage value V E applied to said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2), a relation between the d-axis current value Id, the voltage value V E applied to said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2), and the d-axis equivalent resistance value R d and a relation between the q-axis current value Iq, the voltage value V E applied to said switching elements (13u1, 13u2, 13v1, 13v2, 13w1, 13w2), and the q-axis equivalent resistance value Rq are stored as said relations in said storage part, said d-axis equivalent resistance value R d and said q-axis equivalent resistance value Rq are read from the storage part based on the voltage value V E determined by said voltage detector and said d-axis current value Id and q-axis current value Iq determined by said phase current coordinate conversion part, a d-axis target applied voltage value V d and a q-axis target applied voltage value Vq are determined as said target applied voltage values from the following formulas and V d = R + PL d ⋅ I d * ⋅ ω ⋅ L q ⋅ I q * V q = R + PL q ⋅ I q * ⋅ ω ⋅ L d ⋅ I d * + ω ⋅ Φ a d-axis drop value δV d and a q-axis drop value δV q are determined as said voltage drop values from the following formulas and δV d = R d ⋅ I d δV q = R q ⋅ I q and a d-axis voltage command value V d * and a q-axis voltage command value V q * are determined as said voltage command values from the following formulas and V d * = V d + δV d V q * = V d + δV q in formulas through, R d stands for a d-axis equivalent resistance value, R q stands for a q-axis equivalent resistance value, I d stands for a d-axis current value, I q stands for a q-axis current value, R stands for a predetermined resistance value of said three-phase coils, P stands for a differential operator, L d stands for a predetermined d-axis self-inductance of said three-phase coils, Lq stands for a predetermined q-axis self-inductance of said three-phase coils, I d * stands for a d-axis current command value, I q * stands for a q-axis current command value, w stands for an angular velocity of said rotor, and Φ is a value predetermined by multiplying a maximum value of magnetic flux linkage of said three-phase coils by (3/2) 1/2.