A shock-absorbing elastic sheet comprises a single sheet of elastic material having a flat sheet-like base portion and a large number of semispherical protrusions integral with and projecting from one surface of the flat base portion. The pipette nozzle includes a body defining a passage therethrough. The second crosspiece rods are disposed in the second kite. The locking device is arranged to lock the hammer following a single strike of the hammer against the gong in a strike mode. The interchangeable molds are demountably mounted in common mold and have upper cavities aligned respectively with the through cavities.