An aqueous liquid of a carbon fiber precursor treatment agent contains a carbon fiber precursor treatment agent and water, the carbon fiber precursor treatment agent containing an amino-modified silicone and a particular nonionic surfactant having a molecular weight distribution (Mw/Mn) of from 1.05 to 1.50. The amino-modified silicone may have a kinematic viscosity at 25° C. of 50 to 4,000 mm2/s. The carbon fiber precursor treatment agent is adhered to a carbon fiber precursor.