A method of acquiring traveling characteristics of rear blades in a camera having an image sensing element including a plurality of pixels. The method comprising acquiring the traveling characteristics of the rear blades based on an image signal output from a preset partial area of the image sensing element, and storing the acquired traveling characteristics (S34, S36), shifting the partial area to a different position along the traveling direction of the rear blades (S38), and updating the traveling characteristics of the rear blades stored in the storage medium, based on an image signal output from the partial area shifted to the different position (S35, S36).