A building machine, especially a road finishing machine, comprising a presence detection system. The presence detection system comprises a sensor which is integrated in the control panel of the building machine. By means of the sensor a distance measurement can be carried out, which determines whether the operator is properly seated on the driver's seat of the building machine or whether he stands properly at the standing work place. In order to determine the presence a tolerance range may be specified, which allows a slight movement of the operator on the driver's seat. If the operator approaches the limits of the tolerance range he is asked in time by warning signals to be seated again properly on the driver's seat or adopt a proper position at the standing work place. If the sensor detects no operator on the driver's seat or at the standing work place all of the functions of the building machine are stopped in order to make sure that the work site is safe.