To provide a speed sensorless vector controller which can achieve quick and smooth start, and to provide its control method.

The speed sensorless vector controller comprises a current controller 3, a PWM control inverter 2, the same dimension flux observer 4 and speed estimation mechanism 7 for estimating/outputting a first motor flux and a first motor speed, a slip calculator 5, an adder 17 outputting a primary frequency command value, an integrator 11 outputting a motor flux phase, a speed estimator 30 for estimating/outputting a second motor speed, a current model type flux operating unit 31 for estimating/outputting a second motor flux, and adders 36 and 37 for adding two motor flux phase estimates and outputting a new motor flux estimate.