A method of preparing (meth)acrylic acid by using a reaction distillation apparatus including a reaction distillation tower, and a natural circulation type of heat exchanger as a heat source for the reaction distillation tower. The reaction distillation tower a vessel, where decomposition of Michael adducts occurs, connected to a distillation tower, where distillation of decomposition products occurs. The method includes the following steps: feeding a waste liquid to the reaction distillation apparatus after passing through the heat exchanger, wherein the waste liquid is fed to a lower portion of the heat exchanger via a first input port; feeding a gas, separately from the waste liquid via a second input port, to the lower portion of the heat exchanger, and producing and recovering (meth)acrylic acid while the waste liquid is circulated in the reaction distillation apparatus by the gas which is fed separately from the waste liquid.