PORTABLE TERMINAL DEVICE, CONTROL METHOD, AND CONTROL PROGRAM

PROBLEM TO BE SOLVED: To calculate the distance of a subject within relatively small error in an incorporated camera device, even in a case where based on an amount of movement of a focus lens and an amount of change in refractive index, control such as extending or shortening a focal distance is repeatedly exerted.SOLUTION: The portable terminal device comprises: a focus lens driving section 23 configured to change a focal distance by driving the focus lens 21; a focusing control section 31 configured to control the focus lens driving section 23 so that a focus is brought on a subject based on an output signal from an imaging section 22; an initial setting section 33 configured to set a driving state of the focus lens 21 to an initial state when the control history of the focus lens driving section 23 satisfies a predetermined condition; a focus lens driving state calculating section 34 configured to calculate the driving state of the focus lens based on the control history of the focus lens driving section 23; and a distance calculating section 36 configured to calculate the distance of a subject based on the driving state of the focus lens calculated by the focus lens driving state calculating section 34 when the focus is brought on the subject.