A method for measuring space width of joint includes: a joint image input step of inputting an image of a joint; a contour detecting step of detecting contours of a pair of bones constituting the joint; a measurement range setting step of setting a measurement range of a space of the joint based on the contours detected in the contour detecting step; a space width calculating step of calculating a space width which is a distance between the pair of bones within the measurement range set in the measurement range setting step; and a display step of displaying the space width calculated in the space width calculating step.