A molecular orbital computing device, method, program, and a recording medium recorded with the program, capable of computing electronic states at a high speed by an elongation method, are provided. A molecular orbital computing device (1) for determining molecular electronic states by the elongation method implements a localization process of transforming a canonical molecular orbital by an atomic orbital basis into a regional localized molecular orbital by using the formulas expressed by: YCMORLMO=CROCML+U CAORLMO=CAOCMOYCMORLMO where YCMORLMO is a transformation matrix for transforming into a regional localized molecular orbital by a canonical molecular orbital basis, CROCMO+ is a transpose matrix of a matrix representing a canonical molecular orbital by a regional atomic orbital basis, U is a transformation matrix for erasing elements in an off-diagonal block in a density matrix DRO by the regional atomic orbital basis by a Jacobi method, CAORLMO is a matrix representing a regional localized molecular orbital by the atomic orbital basis, and CAOCMO is a matrix representing the canonical molecular orbital by the atomic orbital basis.