To provide a face direction warning device for reducing unnecessary warning while driving straight and a warning method of the face direction warning device.

The face direction warning device 10 has: face direction detection means 11 and 12 for detecting the degree of face direction of a driver; a looking aside detection means 15a for detecting the driver's looking aside when a prescribed determination criterion is satisfied; and warning means 17 and 18 for warning the driver when the driver's looking aside is detected. The warning device has: lane dividing line recognition means 13 and 14 for recognizing lane dividing lines dividing driving lanes; and a determination criterion control means 15b for making the determination criterion variable depending on whether or not the lane dividing lines are recognized by the lane dividing line recognition means 13 and 14 in a normal state.