Abstract: A brake disc includes an annular disc body and fins. The fins are radially disposed on a back surface of the disc body. At least one of the fins have a bolt hole at a central portion of the fin in a radial direction of the disc body. The disc body includes an inner circumferential portion. The inner circumferential portion is positioned inward from the bolt hole in the radial direction. The inner circumferential portion decreases in thickness as the inner circumferential portion extends inward in the radial direction. The fins each include a top surface and a convex portion. The convex portion protrudes inward from an imaginary plane in the radial direction. The imaginary plane passes an end portion of the top surface and an inner circumferential edge of the back surface.

Abstract: Video data indicating a scene of a surveillance area is produced by a surveillance camera and is compressed to high-compressed video data and low-compressed video data. The low-compressed video data having a large data volume is stored in a storing unit, and the high-compressed video data having a small data volume is transmitted to a surveillance apparatus through a communication line at high speed. Also, in cases where the occurrence of an unusual condition is detected by a detector, an unusual condition detecting signal is transmitted to the surveillance apparatus. In the surveillance apparatus, the high-compressed video data is expanded, and a low-definition scene image of the surveillance area is displayed as a real time image. When the unusual condition detecting signal is received, the signal is displayed, and a watchman can notice the occurrence of the unusual condition.