A cap (10) for a cultivation bottle for brown beech mushrooms includes a cylindrical member (20) that is fitted onto a wide-mouth part (54) of a cultivation bottle (50). The cylindrical member (20) includes a large-diameter cylindrical part (22) that covers and is fitted to an end edge of the wide-mouth part (54) and an outer surface in a vicinity of the end edge, a small-diameter cylindrical part (24) that has a first opening (21) with a smaller diameter than the large-diameter cylindrical part (22), and that is positioned toward a center of the large-diameter cylindrical part (22), and a connecting part (25) that connects an outer peripheral edge of the large-diameter cylindrical part (22) with the small-diameter cylindrical part (24). A height of an inner surface (15) of the small-diameter cylindrical part (24) is from 6 mm to 30 mm.
