An object is to provide an acid-type carboxymethylated cellulose nanofiber in which the viscosity is not excessively high at the time of preparing a dispersion liquid and the introduced carboxymethyl group is desalted to convert the acid type, and the acid-type carboxymethylated cellulose nanofiber has 0.01 to 0.50 of the degree of substitution with carboxymethyl group per glucose unit, wherein the B-type viscosity in an aqueous dispersion with a concentration of 0.95 to 1.05% by mass is 1000 mPa·s or more under the condition of 60 rpm and 20° C., and 7000 mPa·s or more under the condition of 6 rpm and 20° C.