The present invention has a computation device for measuring the dimensions of patterns formed on a sample on the basis of a signal obtained from a charged particle beam device. The computation device has a positional deviation amount calculation unit for calculating the amount of positional deviation in a direction parallel to a wafer surface between two patterns having different heights on the basis of an image acquired at a given beam tilt angle; a pattern inclination amount calculation unit for calculating an amount of pattern inclination from the amount of positional deviation using a predetermined relational expression for the amount of positional deviation and the amount of pattern inclination; and a beam tilt control amount calculation unit for controlling the beam tilt angle so as to match the amount of pattern inclination. The pattern measurement device sets the beam tilt angle to a calculated beam tilt angle, reacquires an image and measures the patterns.