A shape optimization method of a plate-like member which has a concavo-convex shape and includes: identifying a bend stress point where a bend stress is higher in a mode where a specific load is applied to the plate-like member; identifying a bend axis from a distribution of stress vectors around the bend stress point; identifying, in an orthogonal surface to the bend axis, a pair of membrane stress points where a ratio of a membrane stress to a sum of the bend stress and the membrane stress is higher; calculating an offset variable which is a distance between a line segment connecting the pair of the membrane stress points and the bend stress point; and identifying a shape of the plate-like member so as to minimize the offset variable.