A transmission structure of a woodworking lathe contains: a case, a driven gear, a first gear set, a second gear set, and an adjustment lever. The case includes a transmission shaft, a variable speed shaft, and a driven shaft. The driven gear is fixed on the variable speed shaft and meshes with the transmission gear. The first gear set contains a first gear and a third gear which is coaxial with the first gear. Diameters of the first gear and the third gear are different. The second gear set is disposed on the variable speed shaft and contains a second gear and a fourth gear, a diameter of the second gear corresponds to a diameter of the first gear, and a diameter of the fourth gear corresponds to a diameter of the third gear. The adjustment lever is defined between the second gear and the fourth gear.

A speed change auxiliary device of a lathe is provided. A side chamber of the lathe is provided with a shaft seat and a bottom shaft seat at the top and bottom thereof. An auxiliary device is provided between the shaft seat and the bottom shaft seat. The auxiliary device includes a shaft. A spring, an eccentric block, an engaging member, a positioning nut, a rotary sleeve and a fixing block are fitted on the shaft. The rotary sleeve includes a handle. Two sides of an inner circumferential surface of the rotary sleeve have protrusions. The protrusions each have an upright surface and an upper guide bevel at two sides thereof. The fixing block is disposed on the bottom shaft seat. Two sides of a circumferential surface of the fixing block have recesses. The recesses each have a stop surface and a lower guide bevel at two sides thereof.

A speed change auxiliary device of a lathe is provided. A side chamber of the lathe is provided with a shaft seat and a bottom shaft seat at the top and bottom thereof. An auxiliary device is provided between the shaft seat and the bottom shaft seat. The auxiliary device includes a shaft. A spring, an eccentric block, an engaging member, a positioning nut, a rotary sleeve and a fixing block are fitted on the shaft. The rotary sleeve includes a handle. Two sides of an inner circumferential surface of the rotary sleeve have protrusions. The protrusions each have an upright surface and an upper guide bevel at two sides thereof. The fixing block is disposed on the bottom shaft seat. Two sides of a circumferential surface of the fixing block have recesses. The recesses each have a stop surface and a lower guide bevel at two sides thereof.