In the East Japan Railway Company, the system of movable set-off equipment and train protection equipment has been improved. The system has a movable detector that transmits information to the controller about the status of the attachment and detachment of the set off material, but there have been reports of malfunction events such as failures due to repeated impacts from the train and poor installation and adjustment. Therefore, we analyzed the failure events and structure of the detector and made improvements to improve durability, workability, and reduce the risk of failures.