To provide a device and a method of stably manufacturing products of high quality by measuring a moisture percentage of acetate tow online, changing a drying condition of a dryer on the basis of the moisture percentage, and keeping the moisture percentage of acetate tow within a specific range.

This moisture control device of acetate tow is composed of a device for measuring the moisture percentage of acetate tow during traveling, and a device for changing the drying condition of the dryer on the basis of the measured moisture percentage. This moisture control method of acetate tow comprises measuring the moisture percentage of the traveling acetate tow when acetate tow is continuously conveyed from a drying process to a packing process, and changing the drying condition in the drying process on the basis of the obtained moisture percentage.