A motor control device is provided, wherein an electric power (P) consumed
by the brushless DC motor is inferred from three parameters including
motor phase currents (I) flowing through at least two phases of three
phases of the brushless DC motor, motor phase voltages (V) applied to at
least two phases which of the three phases, are the same in phase as the
motor phase currents (I) flowing through the two phases, and a motor
rotational angle (.theta.). Then, the value of a power supply current
(Ib) supplied to the three-phase inverter is inferred based on the
electric power (P) inferred to be consumed by the brushless DC motor and
the power supply voltage (Vb) applied to a three-phase inverter. In
accordance a flow chart shown in FIG. 3, the consumed electric power (P)
is inferred by an expression (1) at step 337, the power supply current
(Ib) is inferred by an expression (2) at step 338, and the inferred power
supply current (Ib) is output to make it possible to detect the
overcurrent supplied to the three-phase inverter.