In this investigation three different experiments on the cylinder vibration caused by the wake force are undertaken. Namely, in the first place on the elastically supported cylinder in a wind tunnel and in the second place on the oscillated cylinder in a model basin experimental studies are undertaken. And in the third place on the oscillated cylinder in a wind tunnel an experimental research is made in which a fluctuating pressure on the cylinder surface is measured. According to these experimental results it is concluded that the exciting mechanism is a selfinduced vibration. In other words the exciting force is caused by the cylinder vibration itself under the special flow velocity, say, the nondimensional velocity of about 5. In addition, the theoretical analysis under this consideration is shown to be able to explain these test results well.