In a resin double-helical gear formed by injection-molding, smooth meshing of teeth can be performed for rotation of the resin double-helical gear in both directions, and occurrences of thrust-direction load and noise can be prevented.Peak-side tooth flanks 7c and 7d and valley-side tooth flanks 7e and 7f of a tooth 7 in a resin double-helical gear 1 are formed such as to become farther away from peak-side tooth flanks 9c and 9d and valley-side tooth flanks 9e and 9f of a standard tooth 9 in an inward direction, the closer the peak-side tooth flanks 7c and 7d and the valley-side tooth flanks 7e and 7f are to a tooth width direction center section 3 from one tooth width direction end section 4a and another tooth width direction end section 4b. As a result, meshing escape sections g (g1 and g2) and h (h1 and h2) having dimensions in a tooth thickness direction that increase towards the tooth width direction center section 3 are formed on the peak-side tooth flank side and the valley-side tooth flank side.