To provide an RTL description model changing device that can change an RTL description mode generated by hand into an RTL description mode suitable for composition of a logic circuit that has high processability and can perform high-speed processing.

This RTL description model changing device 2 that changes a 1st RTL description model whose logic circuit has its operation described in a hardware language including a 1st conditional branch part that has branches and is described with an 'if-else if' statement is that logic composition using a logic composing tool is performed efficiently, and equipped with an analyzing means 22 which detects 1st conditional branch parts described with 'if-else if' statements in the 1st RTL description model and a changing means 24 which changes at least one of detected 1st conditional branch parts into a 2nd conditional branch part described with a case statement.