<p>Holometabolous insects have imaginal discs, which are the pouch-like organs consists of monolayer epithelium, on their larval stages. Larvae unfold imaginal discs during pupation and form the exoskelton shape such as horns and limbs. In order to store the large exoskelton shape of adults in small body of larvae, imaginal discs are folded. Surprisingly, the structure of the imaginal disc is formed by folding the epithelial tissue from the planar shape autonomously. In developmental process of imaginal discs, epithelial sheet grows by cell proliferation and out-of-plane deformation is occurred. This deformation is affected not only by cell activities such as cell proliferation, but also by surrounding tissue. On the apical side of Drosophila leg disc, a kind of imaginal discs, squamous epithelium called peripodial membrane adheres to the disc. Due to this adhesion, out-of-plane deformation of growing leg disc is constrained. In this study, we investigate the mechanical effect of the deformation constraint by surrounding tissue using multicellular dynamics simulation based on 3D vertex model. Simulation results suggest that folding structure which has short wavelength is formed when constraining force from the surrounding tissue is acted on the disc. In addition, we examined the mechanism of folding structure formation from the viewpoint of minimizing mechanical energy. Our examination suggests that wavelength of folding structure is determined from the balance between the bending of the epithelial sheet and out-ofplane deformation of the surrounding tissue.</p>