To efficiently produce carboxymethyl cellulose, the aqueous solution of which has a high viscosity.

In a method for producing carboxymethyl cellulose, after starting material pulp is subjected to a crushing treatment using a crusher, cellulose in the material obtained by the crushing treatment is reacted with a monohaloacetic acid or a salt thereof and an alkaline agent at 40 to 100°C. The method includes a step of mixing the monohaloacetic acid or a salt thereof and/or the alkaline agent with the starting material pulp before or during the crushing treatment of the starting material pulp.