1. A substrate detection device, comprising: a converting unit configured to calculate a gray scale of a gray image of a circuit lead region of a substrate based on the gray image of the circuit lead region of the substrate, and to convert the gray image into an image of leads in the circuit lead region, based on a difference between the calculated gray scales of the leads and of the substrate in the circuit lead region, wherein the leads do not intersect each other; and a judging unit configured to judge a state of the leads in the circuit lead region based on the image of the leads in the circuit lead region, wherein the judging unit is configured such that gray scale values of a plurality of points or portions of the lead are compared with a first predetermined gray scale value and if a difference between a gray scale value of any point or portion of the lead and the first predetermined gray scale value is greater than or equal to a first predetermined threshold value, it is judged that the lead is broken at the point or portion, wherein: the judging unit is configured such that gray scale values of a plurality of points or portions of a strip section, located between adjacent ones of the leads, of the substrate are compared with a second predetermined gray scale value and if a difference between a gray scale value of any point or portion of the strip section, located between adjacent ones of the leads, of the substrate and the second predetermined gray scale value is greater than or equal to a second predetermined threshold value or if the gray scale value of the point or portion of the strip section, located between adjacent ones of the leads, of the substrate is less than the second predetermined gray scale value by the second predetermined threshold value or more, it is judged that the strip section is broken at the point or portion and thus that the adjacent ones of the leads overlap each other.