1. A method for calculating a height of a chuck top, wherein when electrical characteristics of a target object mounted on the chuck top of a probe device are inspected, XY coordinates of at least five points including a center point of a top surface of the chuck top and right, left, upper and lower points thereof are specified by a computer on an XY coordinate plane on the computer; heights of the chuck top which correspond to the specified coordinates are measured sequentially; coordinate transformation formulas for converting the XY coordinates to coordinates including the heights of the top surface of the chuck top are obtained for four quadrants of the XY coordinate plane respectively, and a height of the top surface of the chuck top which correspond to an arbitrary position specified on the XY coordinate plane by the computer is calculated in each of the four quadrants based on the coordinate transformation formulas, the method comprising: setting, by using the computer, a conical model in which two adjacent points other than the center point of the chuck top which correspond to the specified coordinates in a predetermined quadrant of the XY coordinate plane are obtained on a circumference having the center point of the chuck top as the origin; and specifying an arbitrary point in the predetermined quadrant by using the computer and calculating a height of the arbitrary point of the chuck top based on the conical model, the coordinate transformation formulas and the specified coordinates.