Portable grinding device

A grinding device, comprising:

• a body configured as a hollow barrel having an opening, a first fixing element positioned close to said opening, and an external thread configured on an outer wall of an end close to said opening of said body;
• an inner cap configured to mount to an inner wall of an end close to said opening of said body having a second fixing element corresponding to said first fixing element;
• wherein said second fixing element is configured to anchor with said first fixing element;
• wherein an aperture is provided on said inner cap, and a first leak-proof seal is configured to surround said aperture;
• an outer cover having an inner thread, a second leak-proof seal and a projection;
• wherein said inner thread is configured to lock with said external thread of said body, and thereby said second leak-proof seal is made joint said first leak-proof seal for leak-proofing;
• and
• a grinding element positioned inside said body and capable of moving therein freely;
• wherein an area of any cross section of said grinding element is bigger than said aperture of said inner cap.