To provide a manufacturing method for a rubber molded body for a belt capable of forming an accurate joint part by straightly, quickly and accurately cutting a cog crest of the rubber molded body such as a cog pad without depending on a skilled worker.

The cog pad 10, i.e., the rubber molded body alternately having a cog crest 11 and a cog bottom 12 is formed using a mold 4 with a cog and the cog pad 10 is installed on a base 15 so that the cog crest 11 is directed to a back side. A pair of separated retaining molds 17, 17 is fitted to the cog crest 11 and the cog bottom 12 of the cog pad 10 and a pressing member 22 formed with a slit 23 for storing a cutter 20 is press-contacted with the back surface of the cog pad 10. Thereafter, the cutter 20 is stored in a gap of the retaining mold and the slit 23 of the pressing member 22, cuts one cog crest 11 of the cog pad 10 on its central line while moving in the width direction of the cog pad 10 and further cuts the other cog crest 11 at its central part similarly to the above.