A structure determination unit (112) obtains an operational description (511) and determines a candidate of a circuit structure applicable to a plurality of execution units as a structure candidate, the operational description (511) describing an operation of a circuit and including the plurality of execution units. A decision unit (113) calculates, as a circuit characteristic (522), a characteristic of the circuit when the circuit structure of the plurality of execution units is the structure candidate and outputs the structure candidate as a determined circuit structure (310) when the circuit characteristic (522) meets a threshold (521). A high level synthesis unit (140) performs high level synthesis on the operational description (511) so that the circuit structure of the plurality of execution units becomes the determined circuit structure (310).