: As smart phone became popular, its excessive uses cause adverse effects called smart-phone syndrome such as Turtle-neck syndrome in physical side and smart-phone addiction in mental aspects. Turtle-neck syndrome incurred by incorrect posture when you watch smart-phone, which causes a serious health problems. However, these syndromes can be detected by gyro-sensor and timer, and prevented by correcting the posture and halting the function with smart-phone application (App). Thus, this paper proposes App that helps user to realize bad posture and addiction to smart-phone, and to acquire the correct habit by inducing user to stretch neck or to stop operation with warning message. If we tried to adjust bad posture and addiction in using smart-phone through this application, the social losses from smart-phone syndrome would be minimized as a result.