A modularized document handler comprising: a modularized validator for validating a document, a modularized stacker for stowing the document sent from the validator, and a modularized drive device for transporting the document from the validator to the stacker through an intermediate path formed in the drive device, wherein the drive device comprises a drive unit, a case for accommodating the drive unit, and an output gear rotatably supported in the case, the drive unit comprises an actuator, a power transmission device driven by the actuator, a transport device driven by drive power of the actuator through the power transmission device, anterior and posterior gears (11, 12) both driven by drive power of the actuator through the power transmission device, the validator comprises a conveyer device for conveying the document to the drive device along a passageway formed in the validator, and a housing for encasing the conveyer device, the stacker comprises a carrier device for transporting the document from the intermediate path in the drive device to the stacker, the document is consistently transported from the passageway in the validator through the intermediate path in the drive device to the stacker, the housing of the validator is detachably attached to the case of the drive device to disengageably and drivingly connect the conveyer device of the validator to the drive device and to drive the conveyer device of the validator by drive power of the actuator, the stacker is detachably attached to the drive device to disengageably and drivingly connect the carrier device of the stacker to the posterior gear in the drive unit to drive the carrier device of the stacker by drive power of the actuator, characterized in that the modularized document handler comprises a support frame formed with a pair of hinges for sustaining the actuator and power transmission device as a single drive unit, the case of the drive device is formed with a pair of bearings capable of detachably and rotatably receiving the hinges of the support frame, the drive unit is mounted within the case by fitting the hinges into the mating bearings and then rotating the drive unit toward inside of the case, wherein the anterior gear of the drive unit is automatically and disengageably brought into engagement with the output gear of the drive device when the drive unit is rotated to a predetermined fixed position in the case of the drive device. a modularized validator for validating a document, a modularized stacker for stowing the document sent from the validator, and a modularized drive device for transporting the document from the validator to the stacker through an intermediate path formed in the drive device, wherein the drive device comprises a drive unit, a case for accommodating the drive unit, and an output gear rotatably supported in the case, the drive unit comprises an actuator, a power transmission device driven by the actuator, a transport device driven by drive power of the actuator through the power transmission device, anterior and posterior gears (11, 12) both driven by drive power of the actuator through the power transmission device, the validator comprises a conveyer device for conveying the document to the drive device along a passageway formed in the validator, and a housing for encasing the conveyer device, the stacker comprises a carrier device for transporting the document from the intermediate path in the drive device to the stacker, the document is consistently transported from the passageway in the validator through the intermediate path in the drive device to the stacker, the housing of the validator is detachably attached to the case of the drive device to disengageably and drivingly connect the conveyer device of the validator to the drive device and to drive the conveyer device of the validator by drive power of the actuator, the stacker is detachably attached to the drive device to disengageably and drivingly connect the carrier device of the stacker to the posterior gear in the drive unit to drive the carrier device of the stacker by drive power of the actuator, characterized in that the modularized document handler comprises a support frame formed with a pair of hinges for sustaining the actuator and power transmission device as a single drive unit, the case of the drive device is formed with a pair of bearings capable of detachably and rotatably receiving the hinges of the support frame, the drive unit is mounted within the case by fitting the hinges into the mating bearings and then rotating the drive unit toward inside of the case, wherein the anterior gear of the drive unit is automatically and disengageably brought into engagement with the output gear of the drive device when the drive unit is rotated to a predetermined fixed position in the case of the drive device.