To miniaturize a mechanism for driving, to prevent the generation of noises caused by a switching operation, and to improve durability in the damper mechanism of a wave forming device.

In the cylindrical peripheral wall of a casing 20, a first opening 21 communicated with a blower 13, a second opening 23 communicated with the air chamber 3 of a wave forming room 2, and an exhaust port 25 communicated with the outside are formed, a switching blade 30 extended in both blade shape to partition the inside the casing 20 is fixed to an blade shaft 26 concentric with the casing 20, and by using an actuator to change the rotational position of the switching blade 30, switching is made between an air supply state for communicating the first and second openings 21 and 23 with each other and an exhaust state for communicating the second opening 23 with the exhaust port 25.