A tensioner arm comprises a tool-engagement portion for engaging with a tensioner-arm rotation tool, and a jig-holding portion which has a through hole for accepting a tensioner-arm fixation bar jig being inserted thereinto from above at a portion of the tensioner arm extending upward from the base end portion. And information in a non-restored area in the first storage device and information in a second storage device are restored by using information stored in the storage devices other than the first and the second storage devices when the second storage device fails while the information in the first storage device is being restored. The monitoring optical elements are preferably disposed in the end portions of the array for the beam tilt determination.