[Object ]To provide a position-information specifying method for accurately specifying a position and a velocity of a photographed object.[Solution ]A position-information specifying method includes; a step for obtaining an object image 3 photographed by a monitor camera 2 having a predetermined distortion characteristic, a predetermined distortion being caused on the object image 3 due to the predetermined distortion characteristic; a step for obtaining a first scale plate image 42 corresponding to an image obtained when a first scale plate 4 having a first scale 41 is arranged at a first distance X is photographed by the monitor camera 2; a step for overlapping the first scale plate image 42 and the object image 3 with each other; a step for measuring an image-size A of a first reference object 5, which is appeared on the object image 3 and has a first predetermined size B, by using the first scale 41 of the first scale plate image 42; and a step for calculating a first target distance Y between the monitor camera 2 and the first reference object 5, based on the image-size A of the first reference object 5, the first predetermined size B, and the first distance X.