A gall midge that induces conical leaf galls on wild Vitis Linnaeus (Vitaceae) species in Japan was previously identified based on the gall shape as the Nearctic Schizomyia viticola (Osten Sacken) (Diptera: Cecidomyiidae: Cecidomyiinae: Asphondyliini: Schizomyiina). In 2016, leaf galls were newly found on cultivated Vitis coignetiae Pulliat ex Planchon cultivar Suzumi-murasaki and the wild V. coignetiae, Vitis flexuosa Thunberg, and Vitis ficifolia Bunge in northern Japan. Morphological studies of the larvae and adults obtained from the galls revealed that they were an undescribed taxon distinct from the Nearctic species and did not belong to any known genera of Schizomyiina. A new genus, Ampelomyia Elsayed and Tokuda, is erected for Ampelomyia conicocoricis Elsayed and Tokuda new species. The new genus can be distinguished from other genera of Schizomyiina by having ventroapical extension on tarsomere I, the larval abdominal segment VIII with a posterodorsal lobe, and dorsally shifted pair of larval pleural papillae. Molecular phylogenetic analysis supports this taxonomic treatment. In addition, we also place three Vitis-associated Nearctic species in the new genus: Ampelomyia viticola (Osten Sacken) new combination, A. vitiscoryloides (Packard) new combination, and A. vitispomum (Osten Sacken) new combination.