There is provided: a (meth)acrylic acid (salt) polymer which has high properties and is little colored; and a process which can produce this polymer with a high polymerization conversion without causing the corrosion of the reaction vessel. When a (meth)acrylic acid (salt) polymer is obtained by carrying out polymerization of an unsaturated monocarboxylic monomer (a) and an unsaturated polyalkylene glycolic monomer (b) with a polymerization initiator, either a redox polymerization initiator including hydrogen peroxide and a reducing agent is used as the polymerization initiator in a specific amount, or the unsaturated polyalkylene glycolic monomer is subjected to the polymerization in the form of an esterification reaction product as obtained by a process including the steps of: esterifying the unsaturated monocarboxylic monomer and a polyalkylene glycol in a specific charging ratio in the presence of an acid catalyst in a manner for a portion of the residual unsaturated monocarboxylic monomer as a starting raw material to remain; and then neutralizing the acid catalyst and the residual unsaturated monocarboxylic monomer (a) with a basic substance after the esterification; and the polymerization is carried out under conditions where the pH during the polymerization is in the range of 3.2 to 7.0.