A protective member protects an objective lens. The protective member includes an insertion opening through which an objective lens is configured to be inserted and a main body configured to cover the inserted objective lens. The main body includes a side wall portion connected to the insertion opening and a bottom portion connected to the side wall portion as well as facing the insertion opening, and covers the inserted objective lens with the side wall portion and the bottom portion. The protective member further includes a liquid disposed inside the main body, a sealing film body for sealing the insertion opening and a window arranged in the bottom portion of the main body, through which light transmits. The protective member can simplify the work.