PURPOSE: To prevent the dislocation of the connection between a cylindrical container and a cylindrical cap and the generation of clearance between them, and improve the grinding accuracy of a grinding container by forming a male and female screws, which are respectively made of square thread to be engaged with each other, in the peripheral end of each opening of a cylindrical container and a cylindrical cap.

CONSTITUTION: A male screw 11 made of square thread is formed in the periphery of the opening end 1a of a cylindrical container 1. On the other hand, a female screw 21 made of square thread is similarly formed in an inner peripheral groove 20 of the opening end 2a of a cylindrical cap 2. The male screw 11 and the female screw 21 are engaged with each other to connect the cylindrical container 1 and the cylindrical cap 2. Namely, the opening end 1b of the cylindrical container 1 and the wall part 20a of the inner peripheral groove 20 of the cylindrical cap 2 are made to abut on each other. A grinding container with this structure houses the material to be ground such as crystal and the abrasive grains, and the material to be ground is rubbed against the inner wall of the container for grinding by rotating the grinding container. Dislocation of the connection between the cylindrical container 1 and the cylindrical cap 2 and the generation of clearance between them are thereby prevented.