A coating machine serves to directly or indirectly apply a liquid or viscous coating medium onto a moving surface. A coater imbedded in a coater bed, defines in part the metering slot. A limiting surface at the moving surface inlet of the coater bed forms, together with the moving surface, an accumulator chamber, with the opening facing in the opposite direction with respect to the feed direction. The accumulator chamber gradually reduces its volume, and the coating medium, delivered to the accumulator chamber by the moving surface, accumulates in the area ahead of the metering slot. It further includes pneumatic pressure device to alter the relative position of the limiting surface with respect to the moving surface and thus alter the geometry of the accumulator chamber.