PURPOSE: To obtain a long-sized magnetic tape or the like whose magnetic film has a uniform thickness and a uniform composition consisting of Co and Cr by adding preheated Cr to an evaporating source when a vertically magnetizable film consisting essentially of Co and Cr is formed on a substrate.

CONSTITUTION: A substrate 1 is sent from an unwinding system 3 to a winding system 4 along a drum 2, and a Co-Cr film is deposited on the substrate 1 from a Co-Cr evaporating source 5 by a vacuum deposition method. When the deposition is continued using the source 5, the amount of Cr in the composition of the resulting magnetic film decreases gradually because Cr has higher vapor pressure. In order to prevent the decrease, Cr particles are preheated to ≥400°C with a preheater placed around a Cr feeder 6, and the preheated Cr particles 14 are uniformly added to the source 5 while shaking a Cr feeding pass with a device 7 in the latera direction of the substrate. Thus, a magnetic film having a uniform thickness and a uniform composition can be formed rapidly on the long- sized substrate 1.