To provide an interface conversion system and an interface conversion method and its program for realizing the generality of a standard interface (HL7).

This interface conversion system is provided with a message analyzing means for analyzing a message of standard interface specifications (HL7), and for decomposing it into respective message elements and a message converting means for selecting the message elements based on a preliminarily decided conversion rule, and for configuring a message of unique interface specifications. This interface conversion system analyzes and decomposes the inputted message of standard interface specifications (HL7), and reconfigures and outputs it based on a conversion rule. The message analyzing means is integrated into components so that it is possible for a system person in charge to realize system construction corresponding to the standard interface specifications (HL7) by setting the conversion rule to a specific message.