To reduce manufacturing costs of a water meter, an inner case therefor, a mold for molding the inner case, and an inner unit while improving measurement accuracy and durability of the water meter.

In the inner case 21, an inner surface 22A of an inner tube wall 22 is provided across an introducing hole 29 in the axial direction in the opposite side of a bottom wall 27 in the axial direction and an outer surface 22B of the inner tube wall 22 on the bottom wall 27 side are flush with each other. Accordingly, an outer surface of a mold 61A for an inner face for molding the inner surface 22A of the inner tube wall and a part of a mold 62A for outer face for molding the outer surface 22B of the inner tube wall 22 slide to form the introducing hole 29 at the sliding part. This eliminates a need for sliding pins that are conventionally required, to reduce the manufacturing costs.