In a direct fuel injection diesel engine equipped with a pentroof-shaped piston, a collision angle (α) at which fuel injected in a direction in which the height of the top face of a piston (13) is high collides with a cavity (25) is set larger than a collision angle (β) at which fuel injected in a direction in which the height of the top face of the piston (13) is low collides with the cavity (25). By so doing, in a direction in which the height of the top face is high fuel that has collided with the cavity (25) easily rebounds upward, thus achieving effective combustion by mixing with a large amount of air present in the vicinity of the opening of the cavity (25) where the height is high, and in a direction in which the height of the top face is low it is difficult for fuel that has collided with the cavity (25) to rebound upward, thus achieving effective combustion by suppressing the flowing out of fuel or flame from the opening of the cavity (25) where the height is low, thereby appropriately mixing fuel and air in all directions in the circumferential direction of the cavity and making it possible to improve the engine output and reduce harmful exhaust substances.