To provide a mounting material sticking device for a cover which makes the folding part of the mounting material adhere to the peripheral part of a core material and can finish outstanding angular corner parts surely and clearly.

A folding mechanism 100 feeds a work W with a mounting material 2 stuck to a core material 1, and folds/sticks folding parts 2a, 2b bulging out on the periphery of the work W on the back of the core material. 1. The mechanism 100 is provided with a base 12 on which the periphery of the core material 1 is mounted, and a press member 13 mounted on the upper side of the base 12 and serving as a member for folding/sticking the folding parts 2a, 2b. The press member changes the shape of the cross section of its press surface gradually in the longitudinal direction to press the folding parts 2a, 2b one by one to the back of the core material from the base end side in the width wise direction toward the front end side. A lifting spring 14 for lifting/biasing the base part, a contacting member 23 for making the folding parts contact the side end surface of the core material at each angular corner part of the work, an end surface press roller 42 for pressing the folding parts to the side end surface of the core material, etc., are preferably provided.