The currently used dredging method of scallop harvesting includes problems such as the following: ingress of foreign matter in the shells, harvesting of other sea creatures, and damage to the shells. To address these issues and improve the productivity of harvesting, this study proposes a new harvesting method using a robot arm. A dedicated gripper for scallop harvesting is needed for this harvesting method; however, there are no grippers specifically designed for scallops. Hence, the purpose of this study is to develop a new gripper dedicated for scallops. The harvesting gripper must meet these specifications: minimal sand ingress in the scallops, target selectability, secure gripping, power saving, and pressure resistance. To meet these demands, this study focuses on the phenomenon of negative pressure-induced adsorption with a non-electric spring actuator. We attempted to develop a negative pressure adsorption gripper with a spring structure and conducted a harvesting experiment using the developed gripper in the laboratory. The experimental results indicated that the developed gripper succeeded in gripping scallops.