1. A surface extraction method comprising: a first step of investigating, in a three-dimensional space that is divided into regions having a lattice shape, in units of straight-line rows of the regions, whether or not constituting regions that constitute an object which is shown in the three-dimensional space exist; and a second step of extracting, as surfaces of the object, the constituting regions that exist at ends of a straight-line row and ignoring one or more regions between the end regions, wherein in the first step, when a length, width, and height of the three-dimensional space that is occupied by the object are denoted by “M X ”, “M Y ”, and “M Z ”, straight-line rows in a length direction and a width direction on M Z X-Y planes, M X Y-Z planes, and M Y Z-X planes are investigated.