According to one embodiment, a vapor deposition method is disclosed for forming a nitride semiconductor layer on a substrate by supplying a group III source-material gas and a group V source-material gas. The method can deposit a first semiconductor layer including a nitride semiconductor having a compositional proportion of Al in group III elements of not less than 10 atomic percent by supplying the group III source-material gas from a first outlet and by supplying the group V source-material gas from a second outlet. The method can deposit a second semiconductor layer including a nitride semiconductor having a compositional proportion of Al in group III elements of less than 10 atomic percent by mixing the group III and group V source-material gases and supplying the mixed group III and group V source-material gases from at least one of the first outlet and the second outlet.