To provide a radiation-sensitive resin composition which does not cause pattern sidewall swelling, pattern collapse, etc., in a development process, and to provide a (meth)acrylic acid polymer usable in the composition.

The (meth)acrylic acid polymer is controlled in its solubility in an alkaline solution by the action of an acid and has a specific structure having repeating units each having an ether group. Furthermore, the polymer optionally contains repeating units each having, at the side chain, an alcoholic hydroxyl group having a fluorine atom or having a fluoromethyl group at least at the α position and/or repeating units having a lactone ring at its side chain. The radiation-sensitive resin composition includes the (meth)acrylic acid polymer.