A cable management system includes track units whose tracks are engageable to each other at longitudinal ends to ease installation of the tracks to a wall surface as a chain of longitudinally aligned tracks. The lock springs are arranged parallel to each other in an X-direction. The bracket is mounted to the transition piece and connected to the outer casing. The interlayer dielectric is formed on the pixel portion and the peripheral portion. An outgoing angle of the light outgoing from the boundary surface substantially coincides with an incoming angle at which the light reflected by the reflection marker enters the boundary surface.