Audio content data is used in various modes as materials to easily create a new high-quality audio content. Multiple pieces of audio content data used as material data are prepared in advance in a material data storage device 31. Additional data is added to each piece of the material data and is stored in a material database storage device 32. A controlling unit 10 extracts necessary material data from the material data storage device 31 on the basis of at least one of external information received by a receiving unit 20 and rule information stored in a restructuring rule database storage device 33 in accordance with the additional data to compose a new music piece from the extracted material data.