A container containing a cobalt carbonyl complex and a gas that contains carbon monoxide, and a cobalt carbonyl complex composition comprising a cobalt carbonyl complex and a solvent, wherein the concentration of carbon monoxide dissolved in the solvent is 0.001 to 1 wt %.Since the cobalt carbonyl complex contained in the above container or the above composition can retain its sublimation properties for a long time without being converted into a stable complex, when a cobalt film is formed by chemical vapor deposition using the container and the composition, a high-quality film can be formed by a simple process, and the production cost of the cobalt film can be reduced due to high use efficiency of the precursor.