The present invention provides a steering operation mechanism in which the life of a side brake friction plate is extended by stopping lubricating oil from being retained and rising to a high temperature. Provided is a steering operation mechanism in which: a cylindrical sliding body to which a side gear is integrally molded is fit slidably around a steering operation shaft which is laid horizontally inside an oil bath lubrication-type transmission case; a multi-plate side brake is disposed in the outer periphery of the sliding body; and the sliding operation of the sliding body and the braking operation of the side brake are linked, enabling intermittent operation of power. A sliding body oil flow channel and brake oil flow channel, in which a lubricating oil flows in a radial direction of the steering operation shaft, are formed in the sliding body and side brake respectively, and the two oil flow channels are connected.