This vehicle power transmission provided with a crank-type continuously variable transmission mechanism is provided with: a forward and reverse switching mechanism (S1) arranged between an output shaft (12) and a drive wheel (W); a transmission shaft (13) which fits with the outer periphery of the output shaft (12) so as to allow relative rotation; an auxiliary power transmission means (29) for connecting an input shaft (11) and the transmission shaft (13); a first outer spline (13a) provided on the transmission shaft (13); a second and third outer spline (12b, 12c) provided on the output shaft (13); an inner spline (41a) which can shift between a first state of meshing with the first and second outer splines (13a, 12b), a second state of meshing with the second and third outer splines (12b, 12c) and a third state of meshing with the first through third outer splines (13a, 12b, 12c); and a second one-way clutch (45) which is provided between the output shaft (12) and the second outer spline (12b) and which engages when the rotation speed of the output shaft (12) exceeds the rotation speed of the second outer spline (12b). By this means, an engine brake can be used without having to increase the size of the power transmission in the shaft direction dimension.