A new mechanism (we called "α^+ Type") is developed for the Low Temperature Difference Stirling Engine. Now we have completed a 10kW target power prototype model. It is for use of 300℃ heat source from recovering wasted heat and from biomass direct combustion. The AP1-10/250 engine has unique construction which has a displacer composed two pistons and power piston arranged at center of lower piston of displacer. This mechanism aims for decreasing flow friction of working gas, reducing piston forces and increasing regenerator efficiency. This paper describes the concept and the experimental results obtained by performance test. The engine performs 8640W/600rpm shaft power under heat source temperature of 279℃.