A winding unit (2) of an automatic winder (1) includes a yarn supplying section (11), a winding section (13) that winds a yarn Y supplied from the yarn supplying section (11) around a winding tube (17) into a package, a yarn clearer (22) that detects thickness of the yarn Y, and a unit controller (26). The unit controller (26) includes a yarn length calculating section (41) that calculates the length of the yarn Y wound around the winding tube (17) and a weight calculating section (42) that calculates a yarn weight of the package. The weight calculating section (42) calculates the yarn weight of the package based on the thickness of the yarn Y detected by the yarn clearer (22), the length of the yarn Y detected by the yarn length calculating section (41), and information on the specific gravity of the yarn Y.