This experimental study is about suppression of flow-induced vibration with flexible sheet and characteristics of flow-induced vibration of elastically supported two circular cylinders in side-by-side arrangement. In particular, the characteristics of flow-induced vibration of the two cylinders are investigated with changing flow speed at each spacing ratio L/D (L : space between two cylinders, D : diameter of cylinder). Flow patterns around the vibrating two cylinders are also investigated by flow visualization with reproducing the state of elastically supported vibration accurately in forced vibration apparatus. It is clarified that characteristics of flow-induced vibration of two cylinders are changed with switching flow passing through the two cylinders. The method to suppress the flow-induced vibration of a single cylinder by attaching flexible sheet (21) is also tested for two cylinders side-by-side arrangement. As a result, suppression effect by attaching the flexible sheet on the two circular cylinders in side-by-side arrangement is confirmed.