A Group 5 metal oxide film such as niobium oxide and tantalum oxide is attracting attention as a film having a high refractive index and exhibiting high optical transparency, i.e., as a material for a device such as semiconductor device and optical device. The technique for manufacturing a Group 5 metal oxide film includes, in rough classification, two processes, i.e., a dry process and a wet process. The dry process includes a sputtering method, an ion plating method, an atomic layer deposition method (ALD method), a chemical vapor deposition method (CVD method), etc. The wet process includes a sol-gel method, an organic metal deposition method (Metal Organic Deposition; MOD method), etc. While the dry process requires a special production facility such as large vacuum apparatus, the wet process has a cost benefit in that the process can be performed only with a simple production facility. In the case of manufacturing a film by a wet process, the kind of the film-forming material and the film formation temperature greatly affect the quality of the film obtained. In Non-Patent Documents 1 to 12, a multinuclear niobium complex and a multinuclear tantalum complex, each having an oxo ligand and an alkoxy ligand, are described. The complexes described in those documents are different from the Group 5 metal oxo-alkoxo complex of the present invention in the number of central metals or the number of ligands. In addition, those documents are absolutely silent as to using the complex described in the documents as a film-forming material.