Disclosed is a monitoring circuit responding to different operational conditions of an electric motor. The circuit includes a measuring resistor connected in series with the stator winding of the motor to produce an actual load value signal. The actual value signal is applied to one input of a comparison circuit whose other input is consecutively supplied with three different nominal reference voltages corresponding to principle operational conditions of the motor, namely to the starting phase, to the normal operational phase, and to an overload. The source of the variable reference voltage includes switching transistor cooperating with a timing member and with voltage dividers adjustable from zero to a maximum nominal voltage value corresponding to the power supply voltage.