A vertical heat-treating apparatus which allows effective use of an installation space and improved productivity is disclosed. In this system, a plurality of housings, each accommodated with a vertical reactor, are aligned with each other. A gas feed unit and the like are arranged in front of each housing with a space disposed therebetween for conducting maintenance work. A rail is installed along the rear side of the housings. A boat liner is located on the rail for carrying a boat to the housings. An interface mechanism including a horizontal-vertical conversion handling unit for supplying the boat in a vertical state to the boat liner is disposed near the rail.