A vacuum treating method and apparatus wherein preliminary vacuum chambers which are charged with and discharged therefrom materials to be treated are arranged on both sides of a vacuum treating chamber such that the preliminary vacuum chambers are switchingly communicated with and disconnected from the vacuum treating chamber; the materials are alternately moved between both the preliminary vacuum chambers and the vacuum treating chamber and are subject to vacuum treatment for a predetermined period of time in the vacuum treatment for a predetermined period of time in the vacuum treating chamber; wherein when a material to be treated has been charged from one preliminary vacuum chamber to the vacuum treating chamber and a treated materiala has been discharged from the vacuum treating chamber to the other preliminary chamber, the vacuum treating chamber and both the preliminary vacuum chambers are disconnected from each other, then the pressure within the vacuum treating chamber is reduced to a required degree of vacuum and the pressure with the one preliminary vacuum chamber is reduced to a degree of vacuum higher than that required for vacuum treatment, and in the other preliminary vacuum chamber, after a treated material has been discharged out and a new material to be treated has been charged, the pressure reduction is initiated from an atmospheric state; and wherein after vacuum treatment has been made in the vacuum treating chamber, the vacuum treating chamber and both the preliminary vacuum chambers are brought into communication with each other to move the materials therebetween.