To effectively impart sizing performance to paper, while reducing the amounts of an internal sizing agent and aluminum sulfate, a papermaking additive comprises a mixture of an amphoteric copolymer having a hydrophobic group whose quaternization ratio is 40% by mole or more, and in which the ratio of the anion equivalent to the cation equivalent is 0.1 to 90%, and a calcium carbonate filler. The filler is one in which suitable water repellency is imparted to the filler. Hence, by adding this to pulp slurry, followed by a wet papermaking, the filler is efficiently adsorbed onto pulp fibers having anionic property, so that effective sizing performance can be imparted to the paper by using a smaller amount thereof than the internal sizing agent, while reducing the amounts of the internal sizing agent and the aluminum sulfate.