An expansion device includes: a thermal distension unit configured to thermally distend a thermally-expandable sheet by irradiating the thermally-expandable sheet with predetermined energy; a reading unit configured to read identifiers provided at predetermined positions of the thermally-expandable sheet; and a setting unit configured to set an amount of energy per unit area to be emitted on the thermally-expandable sheet by the thermal distension unit depending on whether (i) a second identifier as well as a first identifier has been read, or (ii) whether a predetermined part of the first identifier has been read but another part has not been read, as a result of reading the identifiers by the reading unit.