To provide a composite power generation device with improved power generation efficiency in which a fuel cell device and a Stirling engine generator are combined.

The composite power generation device is configured as a combination of the Stirling engine generator including a piston container 13 having a piston therein and an expansion space side 26 and a compression space side 27 formed across the piston therein and being filled with an actuation gas for actuating the piston, and a power generating portion for generating power in accordance with the movement of the piston; and the fuel cell device including a fuel cell module 1 storing a cell stack 5 in which each of a plurality of solid-oxide-fuel-cell cells 3 is electrically connected in series. Further, the expansion space side 26 of the piston container 13 is disposed inside a power generation chamber 16 of the fuel cell module 1 storing the cell stack 5, whereby the expansion space side 27 can be efficiently brought to a high temperature to heat the actuation gas efficiently. Whereby, the Stirling engine generator can be driven efficiently to achieve the composite power generation device with improved power generation efficiency.