There is provided a resin cage of a tapered roller bearing. The cage includes a small diameter annular portion, a large diameter annular portion, and a plurality of bar portions arranged at intervals in a circumferential direction to connect the annular portions. The bar portion has a pair of circumferentially-directed side surfaces, each having a roller guide surface, and an inner-side inner peripheral surface, a circumferential width of which is smaller on a side of the large diameter annular portion than on a side of the small diameter annular portion, and has a roller retaining region in which a radially outer side pocket width and a radially inner side pocket width between the opposed circumferentially-directed side surfaces of the adjacent bar portions are smaller than a diameter of the roller.