PURPOSE: A central opening and shutting device is provided, which makes accurate sample dispersion accomplished by operation of the upper plate. CONSTITUTION: A central opening and shutting device is constituted as follows. Four guide projections are formed on upper side corner of the lower plate(10) in which a through-hole(11) is formed. The upper plate(20) is combined to rotate relatively in the guide projection of the lower plate to make the through-hole of the upper plate coincide with the through-hole of the lower plate. Four valve plates(30) are arranged between the lower plate and upper plate. A drive pin is inserted in the straight hole of the lower plate through the pin hole of the valve plate.
