Abstract: In the method and apparatus for obtaining acoustic characteristics of sound of a broad frequency range of from, for example, 0 to 20 KHz in a relatively short time with high accuracy even though an inexpensive computer is used; multiple sound ray vectors are defined; a virtual space is defined by a polygonal boundary; the propagation history data of the vector is calculated and stored, the vector being reflected at the boundary; and, based on the data, as for each of the vectors, a transient response thereof at an observation point is added to a time-series numerical array and stored, the response being determined on the basis of the reflected vector and a velocity potential determined at the observation point by a micro-area element of the vector defined on the boundary.