The present invention relates to a speed transmission device for a hybrid type motor vehicle comprising a primary transmission shaft (34) connected to a thermal engine (10) through a disengaging coupling (38) and carrying at least two primary toothed wheels (50, 52) cooperating with at least two secondary toothed wheels (54, 56) carried by a secondary transmission shaft (36) connected to an axle shaft (20) of the vehicle and to an electric machine (12).According to the invention, one (54) of the secondary toothed wheels is carried by secondary shaft (36) through a one-way coupling (58).