In a previous experiment of a deposition work of depositing a film with a uniform thickness on a long strip base material in the longitudinal direction thereof, an elapsed time from the start of the deposition work and an output of a power supply at the elapsed time are measured. The resulting relation between the elapsed time and the output is stored in a storage device. Subsequent deposition on a long strip base material is performed by a method in which first, the output of the power supply is controlled to be stabilized at a desired value using a crystal oscillator thickness gauge in a pre-heating step before the start of the deposition work, and then, a base material transport device is driven to start the deposition work on the long strip base material after a desired deposition rate is obtained. After the start of the deposition work, the output of the power supply is controlled to coincide with the output at the elapsed time stored in the storage device.