A reverse shift device of a manual transmission is disclosed to reduce the total length of the transmission, improve shift feeling and decrease noise by excluding a reverse idler gear that rotates, while being meshed between input and output axles, the device comprising: an idle axle fixed at a shift case; and an idle synchronizer installed at the idle axle for switching a state of conveying the rotational force of an input axle to an output axle at the time of forward-reverse shifts.