A shift drum drive unit for rotatably driving a shift drum in a straddle type vehicle, the vehicle including an engine configured to generate drive force by fuel combustion, a transmission configured to change, for the drive force of the engine, a rotation speed by a plurality of gear trains forming a plurality of gear stages with different transmission gear ratios from one another, and a shift shaft formed in a shaft shape, protruding from an inside of a crank case forming a portion of the engine, and configured to rotatably drive the shift drum for changing the gear trains of the transmission in the crank case, the shift drum drive unit comprising: a shift actuator configured to rotatably drive the shift drum; a rotary drive body into which the shift shaft is inserted and which is rotatably driven together with the shift shaft by the shift actuator; a power transmission mechanism including two gears engaging with each other and rotatably supported in the unit case with the power transmission mechanism engaging with the rotary drive body and a rotary drive shaft of the shift actuator thereby transmitting the rotary drive force of the shift actuator to the rotary drive body while decelerating such force; and a unit case configured to support the shift actuator and to house an entirety of the rotary drive body in a state in which the rotary drive body is rotatable, wherein the unit case includes an inner case forming the substantially half of the unit case facing the crank case, and an outer case forming the substantially remaining half of the unit case facing the opposite side of the crank case; the inner case supports, on an inner surface thereof, one end portion of each of the rotary drive body and the power transmission mechanism, and the outer case supporting, on an inner surface thereof, the other end portion of each of the rotary drive body and the power transmission mechanism, a portion of the outer surface of the inner case facing the rotary drive body comprises an insertion port, being a through-hole, for inserting the shift shaft into the rotary drive body, and the unit case includes an attachment section (239a-d) for attachment of the unit case to a side wall of the crank case, characterized in that the inner case supports, on an outer surface thereof, the shift actuator with the rotary drive shaft penetrating the inner case and in that the rotary drive body includes a shaft fitting sleeve which is directly and rotatably supported in the unit case and into which the shift shaft is inserted, and an indirect output gear attached to the shaft fitting sleeve to be rotatable together with the shaft fitting sleeve. an engine configured to generate drive force by fuel combustion, a transmission configured to change, for the drive force of the engine, a rotation speed by a plurality of gear trains forming a plurality of gear stages with different transmission gear ratios from one another, and a shift shaft formed in a shaft shape, protruding from an inside of a crank case forming a portion of the engine, and configured to rotatably drive the shift drum for changing the gear trains of the transmission in the crank case, a shift actuator configured to rotatably drive the shift drum; a rotary drive body into which the shift shaft is inserted and which is rotatably driven together with the shift shaft by the shift actuator; a power transmission mechanism including two gears engaging with each other and rotatably supported in the unit case with the power transmission mechanism engaging with the rotary drive body and a rotary drive shaft of the shift actuator thereby transmitting the rotary drive force of the shift actuator to the rotary drive body while decelerating such force; and a unit case configured to support the shift actuator and to house an entirety of the rotary drive body in a state in which the rotary drive body is rotatable, wherein a shaft fitting sleeve which is directly and rotatably supported in the unit case and into which the shift shaft is inserted, and an indirect output gear attached to the shaft fitting sleeve to be rotatable together with the shaft fitting sleeve.