To easily provide a long sealing tape bent for its upper surface in a non-cured state by pressing a rolling cutter while moving a square sheet, cutting this to obtain a square pillar-like sealing tape and grinding the corner parts of the square pillar-like sealing tape by a rolling grinder.

For manufacturing a sealing tape 10, first, a sealing tape material is made by adding antioxidant or the like to a rubber base material in a material making step 100. Then, in a machining step 200, the sealing tape material is pressed in its non-cured state to make a square sheet 201 and then, in an adhesive sticking step 300, an adhesive sheet 301 having one surface protective tape 302 peeled off is stuck to the bottom surface of the square sheet 201. Then, in a cutting step 400, the square sheet 201 is cut by a rolling cutter 404 to obtain a square sealing tape and the, in a grinding step 500, both corner parts of the upper surface of the square sealing tape are ground and bent to obtain a long sealing tape 10.