A Stirling refrigeration system (1) comprises two Stirling refrigeration units (4a, 4b) incorporating respective working gas end (WGE) heat exchangers (35a, 35b) and radiators (65a, 65b). Cooling water circulates through a first radiator (65a), a first WGE heat exchanger (35a), a second radiator (65a), a second WGE heat exchanger (35a), and a cooling-water pump (67) in sequence. To facilitate deaeration of the cooling-water circuit at time of feeding cooling water, An air release duct (85) is provided at the maximal point of the cooling-water circuit. An air release valve (79) is formed in the open end of the air release duct (85) so that the air remaining in the cooling-water circuit can be easily released. The Stirling refrigeration system is compact in dimensions.