To provide a combustion chamber structure of a diesel engine capable of improving performance thereof throughout a whole region from low rotation to high rotation.

A combustion chamber structure of a diesel engine 10 comprises: a main chamber 18; a subsidiary chamber 20; an injector 22 which injects fuel into the subsidiary chamber 20; and a partition member 25 which has a communication hole 27 communicating the main chamber 18 with the subsidiary chamber 20. The partition member 25 is movable between the main chamber 18 and the subsidiary chamber 20. The combustion chamber structure of the diesel engine 10 also has: an actuator which moves the partition member 25; and an electronic control device which controls the actuator in accordance with an operation state of the diesel engine 10. Thus, the distance of the communication hole 27 to fuel spray injected through the injector 22 is variable when the partition member 25 is moved.