PURPOSE : To speedily and easily calculate the unit area price of a real estate by displaying the corresponding unit area price by rotating a rotary disk as a slide scale where occupation area is entered at specific positions on a substrate, and aligning the occupation area of the slide scale with an estate price on a fixed scale. CONSTITUTION : A substrate 1 provided with a price scale 1a and a unit area price scale 1b and a rotary disk 2 provided with an area scale 2a function as a fixed scale and slide scale respectively. Namely, the rotary disk 2 is rotated on the substrate 1 to align the price scale 1a of the substrate 1 and the area scale 2a of the rotary disk 2 with the estate price and occupation area of object estate, and then the corresponding unit area price scale 1b is displayed at the oppposite position on an indication display 2h in a cut window 2g provided for the rotary disk 2. Consequently, the unit area price of the real estate can speedily and easily be calculated.