A moisture permeability measuring device includes a first body member including a seating part, a flexible bottom plate to be arranged on the seating part, a flexible top plate to be arranged on the bottom plate, a holder part to fix a lower edge portion of the bottom plate and an upper edge portion of the top plate, and a second body member to be arranged on the holder part and having a through-hole defined in a region overlapping the top plate, and an area of the seating part on a plane is smaller than an area of the bottom plate on the plane.