A power transmission mechanism equipped with a first shaft including a first double helical gear, a second shaft including a second double helical gear and a third double helical gear arranged in alignment with the second double helical gear in an axial direction, and a third shaft including a fourth double helical gear that meshes with the third double helical gear. The second double helical gear includes a pair of right and left tooth portions whose torsional directions are reverse to each other such that the left tooth portion and the right tooth portion are offset in phase from each other, and the third double helical gear includes a pair of right and left tooth portions whose torsional directions are reverse to each other such that the left tooth portion and the right tooth portion are identical in phase to each other.