This construction machine drive device is provided with: a reduction gear that reduces the speed of the torque of a motor and transmits the reduced-speed torque to a unit to be driven; and a brake mechanism that generates braking force opposing the torque transmitted by the reduction gear to the unit to be driven. The reduction gear is provided with: a rotational shaft disposed within a casing; and a planetary-gear-type reduction unit having at least one stage and disposed within the casing. The reduction unit has: a sun gear; a ring gear; a planetary gear that meshes with the sun gear and the ring gear; and a spider that supports the planetary gear in a manner so that the planetary gear can rotate. The brake mechanism has: a rotational-shaft-side brake plate provided to the outer periphery of the spider in the state of rotating integrally with the spider; a casing-side brake plate provided to the casing; and a brake piston that generates braking force by means of causing the rotational-shaft-side brake plate and the casing-side brake plate to be pressed in contact with each other.
