A production method of a water-absorbent resin includes the steps of: obtaining a hydrogel by supplying monomer liquid to a reaction device so that the monomer liquid is polymerized; and detaching thehydrogel from the reaction device, wherein the reaction device's surface in contact with the monomer liquid at a position where polymerization occurs is made of a fluororesin having a melt viscosityof less than 1x10<8 >poise at 380 DEG C. On this account, it is possible to obtain a water-absorbent resin having less amounts of an extractable content with high productivity and it is possible to carry out continuous production for an extended period of time.