A segment including a set of blocks necessary to calculate blocks having internal states and blocks having no outputs is extracted by tracing from blocks for use in calculating inputs into the blocks having internal states and from the blocks having no outputs in the reverse direction of dependence. To newly extract segments in which blocks contained in the extracted segments are removed, a set of nodes to be temporarily removed is determined on the basis of parallelism. Segments executable independently of other segments are extracted by tracing from nodes whose child nodes are lost by removal of the nodes in the upstream direction. Segments are divided into upstream segments representing the newly extracted segments and downstream segments representing nodes temporarily removed. Upstream and downstream segments are merged so as to reduce overlapping blocks between segments such that the number of segments is reduced to the number of parallel executions.