In a speed change gear device having a gear shaft (30 in FIG. 1), bearings (32A, 32B), and a housing (21) which accommodates the gear shaft and the bearings therein; lubricating auxiliary vessels (50, 60) are mounted within the housing (21) so as to catch oil scooped up from a collection of oil (P) and to introduce the received oil into the bearings (32A, 32B) not directly immersed in the collection of oil (P). The lubricating auxiliary vessels (50, 60) are arranged at positions which lie laterally and lower than the intermeshing portion of gears (38, 39). The level (PL) of the collection of oil (P) is set at a height at which the lower end (H2) of at least one (39) of the gears is immersed in the collection of oil (P). Due to the location of the lubricating auxiliary vessels (50, 60), the bearings (32A, 32B) are suppled with sufficient quantities of oil even during low-speed rotation of the gear (39).