A polyacrylamide resin has at least one kind of a first unit represented by the following formulas (1) to (4) and a second unit represented by the following formula (5). (In the above-described formulas (1) to (4), R1 represents a hydrogen atom, a methyl group, an ethyl group, or a benzyl group; R2 and R3 are independent and represent a hydrogen atom, a methyl group, an ethyl group, or a benzyl group; and X represents an anion). (In the above-described formula (5), R4 represents a hydrogen atom or a methyl group and R5 represents a hydrogen atom, an alkali metal ion, or an ammonium ion).