To provide a scanner system capable of correctly detecting the position of a form and a method for detecting its subject range.

In a direct scanner system 10, the form is placed on a mat 28 of a direct scanner 12, an imaging section 38 images an incident light via an optical system 36, a pre-processing section 40 processes the obtained image signal into image data 42, supplies the image data 42 to a personal computer (PC) 14, and the PC 14 detects a border of the form on the basis of white grid lines (white lines) included in the supplied image data 42 so as to obtain a range (region) of the form with high accuracy even when a luminance difference between a background color of the mat 28 and the form is insufficient.