A trap mechanism is provided in the middle of an exhaust passage through which an exhaust gas, which is exhausted from a film formation device body that forms a thin film on the surface of a workpiece (W), flows, and recovers a gas to be collected that is contained in the exhaust gas by cooling and liquefying the gas to be collected. The trap mechanism includes: a housing having a gas inlet and a gas outlet; a partitioning member that partitions the inside of the housing into retention spaces; communication paths that communicate the retention spaces with one another; and cooling jackets that cool the communication paths to cool the exhaust gas. With this structure, the exhaust gas is adiabatically expanded while being cooled, and the gas to be collected is efficiently cooled and liquefied.