Abstract: Ventilating device, comprising a fan, an electromotor coupled with the fan for driving the latter, a controllable excitation circuit coupled with the motor, and means for detecting the rotational speed of the fan. These means are adapted for the detection of rotation of the fan under a predetermined minimum speed upon which the excitation of the motor can be adapted. The excitation circuit comprises means for gradually speeding up the fan, departing from the standstill position and means for temporarily increasing up to the maximum of the excitation of the motor in response to the detection of the rotation of the fan under the predetermined minimum speed. As speed detection means a measuring fan is provided.