An apparatus for mixing a high-viscosity material with a gas and transferring the high-viscosity material mixed with the gas. The apparatus includes a piston pump, a high-viscosity material supply device for supplying a high-viscosity material to the cylinder, a gas supply device for supplying a gas to the cylinder, a piston drive device for driving the piston of the piston pump, a piston stopping device fixed in the cylinder for stopping the piston, a valve device for a high-viscosity material for selectively opening and closing a passage for communication between the high-viscosity material supply device and the cylinder of the piston pump, and a valve device for a gas for selectively opening and closing a passage for communication between the gas supply device and the cylinder of the piston pump.