In the reactor core of a Pressurized Water Reactor (PWR), considering abnormal situations such as system pressure drop or loss of coolant flow, they may lead to unexpected subcooled boiling. When subcooled boiling occurs in the core, vapor bubbles generated by subcooled boiling are unstable and soon condensed in bulk water around fuel rods because of temperature difference between vapor bubbles and bulk water. This means that the local pressure change due to vapor bubble generation and condensation is rapidly repeated adjacent to the fuel rods under subcooled boiling conditions. This behavior of vapor bubbles is considered a cause of the fuel rod vibration, so-called a subcooled boiling-induced vibration (SBIV). For understanding on a basic mechanism of the SBIV, some experiments to observe this phenomena and to measure the vibration of a single heater rod in distilled water were performed under an atmospheric pressure and various thermal conditions as parameters of temperature, the degrees of superheat of the rod surface and the degree of subcooling in bulk water. This study investigated the effects on the SBIV of the heater rod due to the existence of a metallic wall which formed a narrow gap of water adjacent to the heater rod. As a result of experiments with various sizes of gap between the metallic wall and the heater rod, it was found that the gap size between the wall and the heater rod could influence the SBIV of the heater rod together with some effects on the heat transfer to the bulk water and on changing of the vibration of the heater rod due to limited amount of the water in the region.