PURPOSE: To provide a locked train type transmission device by making the phases of teeth of gears on both ends of intermediate shafts coincide each other in a very simple constitution, and making the device adaptable to general purpose industrial machines, in a locked train which has three intermediate shafts.

CONSTITUTION: To an input gear 5 and an output gear 7 arranged coaxially opposing each other, intermediate gears 6a and 6b consisting of three gears respectively are engaged, and the intermediate gears opposing each other between the input gear 5 and the output gear 7 are combined by intermediate shafts, so as to compose a locked train type transmission device. And one side of both intermediate gear groups engaged with the input gear 5 and the output gear 7 is formed in an intermediate large gears 6a, and the other side is formed in an intermediate small gear 6b, respectively, the intermediate small gear 6b is connected to the intermediate large gear 6a coaxially through an involute spline with the form same as the gear 6b, and a gear coupling 3 is connected to an input shaft 1.