To provide a new method for detecting the state of an operator operating a portable terminal device.

A portable terminal device 1 operated by the operator comprises: a display part 14 displaying display data 123; an imaging part 15 and an image signal processing part 16 which acquire image data 160 including the face of the operator; a detection part 101 detecting the change of the relative position of the display data 123 displayed on the display part 14 and the face of the operator, based on the acquired image data 160, to create change data 122; a determination part 100 determining whether or not the operator is in the middle of walking; and a display control part 102 controlling the display position in the display part 14 of the display data 123 displayed on the display part 14, so as to suppress the change of the relative position detected by the detection part 101, when the determination part 100 determines that the operator is in the middle of walking.