To prevent approximately completely a phenomenon wherein the main cover surface is damaged by using an exchange cover.

This pit cover 12 is equipped with a transparent main cover 38 having the thickness capable of bearing the weight and an impact, a comparatively-thin transparent exchange cover 32 for covering the upper part of the main cover 38 with a clearance, and transparent liquid 36 filled in the clearance between both covers and sealed in the clearance. The transparent liquid 36 is sealed in a sealed space defined by a sealing material 34 applied along the periphery of the pit cover 12, the main cover 38 and the exchange cover 32. The transparent liquid 36 prohibits direct contact between the exchange cover 32 and the main cover 38. The comparatively-thin exchange cover 32 is supported by silicone oil from below, and is hardly bent even if a weight is applied from above, and is not brought into direct contact with the main cover 38.