To provide a swirl chamber type combustion chamber for a diesel engine capable of increasing air utilization factor in a main combustion chamber.

In the swirl chamber type combustion chamber for the diesel engine provided with a swirl chamber 5 on a cylinder head 5, making the swirl chamber 5 and the main combustion chamber 3 communicated by a port 6, making an injector 7 face to the swirl chamber 5, injecting fuel to the swirl chamber 5 from the injector 7, making part of fuel burn in the swirl chamber 5, making combustion expansion gas containing unburned fuel blowout toward a center part side of the main combustion chamber 3 from an outer circumference edge part side of the main combustion chamber 3 by the port 6, and making the unburned fuel mixed with air in the main combustion chamber 3 and burned in the main combustion chamber 3, an arc shape expansion gas guide groove 8 along an outer circumference edge is provided on the outer circumference edge part of a piston top surface 1, a center part of the expansion gas guide groove 8 is opposed to the port 6 and part of combustion expansion gas blowing out to the main combustion chamber 3 from the port 6 is guided to the outer circumference edge part of the piston top surface 1 by the expansion gas guide groove 8.