To make a slide plate for opening and closing pressure weldable to an attaching plate and block the inflow of useless leak air into a building when the vent hole is closed in a ventilation opening device for controlling the inflow air volume to the building by sliding a slide plate to the attaching plate having the vent hole in the building.

In a ventilating opening device of the building with which the outside air flow volume to the inside of a building B from a vent hole 1a through a movable vent hole 2b can be adjusted by adjusting a slide plate 2 on an attaching plate 1 attached to the building B; by a pushing force adjusting screw 3g of a stride bridge body 3, an elastic pushing plate 4 is bent and contacted to plate portions 2c and 2d at the pressure receiving side of the slide plate 2. In this way, a slide contact plate portion 2a of the slide plate 2 is elastically contacted to the attaching plate 1, and by a running direction controlling portion 5 provided at the leg portions 3a and 3b of the stride bridge body 3, a linear slide in a predetermined running direction D of the slide plate 2 can be guaranteed.