1. A charged particle beam projection method comprising steps of: (a) preparing pattern data for defining a plurality of patterns on a pattern layout plane; (b) assigning an exposure dose for exposing the pattern to each of the plurality of patterns; (c) approximating a deposition energy distribution when a charged particle beam is made incident upon a resist film, by a sum of a plurality of element distributions, each of which is represented by a Gaussian distribution; (d) defining a pattern area density map partitioning the pattern layout plane into a plurality of small regions, with respect to each of at least some element distributions among the plurality of element distributions; (e) repeating sub-steps (e1) and (e2) with respect to each of the pattern area density maps, (e1) obtaining an area density with respect to each small region, the area density indicating a ratio of an area occupied by a pattern disposed in the small region to a whole area of the small region, and (e2) in accordance with an energy deposition rate representative of an influence degree of exposure of a first small region upon a deposition energy to be given to a target small region, an exposure dose assigned to a pattern in the first small region, and an area of the pattern and the area density of the first small region, executing a sequence of obtaining the deposition energy to be given to the target small region, by using each of small regions influencing the target small region as the first region, calculating a corrected area density representative of the deposition energy to be given to the target small region by calculating a sum of deposition energies to be given to the target small region, and correlating the corrected area density with each of all small regions; and (f) calculating the deposition energy at an evaluation point on the pattern layout plane, from the corrected area density calculated in the sub-step (e2).