The invention relates to manual lubricant supply devices, particularly to a grease gun. The grease gun is composed of a grease storage tube and an end cover. The grease storage tube is made of transparent materials, a piston, a piston rod and a spring are arranged inside the grease storage tube, wherein the piston rod axially penetrates the grease storage tube, the spring sleeves the piston rod, the piston rod is connected with the piston, and the piston limits the spring inside the grease storage tube; the grease storage tube is threadedly matched with the end cover, the end cover is made of plastics and provided with a lever type grease output mechanism and a grease outlet pipe; a grease package bottle is arranged inside the grease storage tube and composed of a bottle body and a bottle cover, wherein the bottle body comprises a bottle body unit and a bottle bottom and is flexible, and a plurality of hard ring-shaped portions are formed in the axial direction of the bottle body unit and are higher in hardness than other portions of the bottle body unit. By means of the structure above, the bottle body can avoid inward recession to form extrusion dead zones due to flexible materials, and further waste of lubricating grease inside the dead zones can be avoided.