Conventionally, an apparatus for controlling a shift operation in a transmission has been widely known, and includes a multi-stage synchromesh-type transmission, in which a shift operation can be performed by means of a control signal, and a clutch device, in which a clutch of a clutch assembly can mechanically establish and interrupt transmission of a driving force between a driving power source and the transmission itself in response to a control signal.  This type of apparatus is referred to as an automated manual transmission (AMT).  By virtue of this automated manual transmission, a gear ratio changing operation including a shift operation performed automatically in the transmission as well as automatically performed engagement and disengagement of the clutch. 
In this type of apparatus for controlling a shift operation in a transmission, when the clutch has been disengaged during a shift operation in the transmission, torque from the engine is not transmitted to the vehicle wheels.  In this case, even when a vehicle driver expects or requires acceleration of the vehicle, the achieved degree of acceleration may be virtually zero, and on occasions an impression of a loss in vehicle acceleration can even be created.  Moreover, when the clutch is engaged during a final phase of the gear ratio changing operation, a difference between an engine rotational speed (i.e., rotational speed of a crankshaft) and a transmission input shaft rotational speed can occur due to factors such as an excessive rotational speed of the engine, thereby on occasions resulting in an excessive degree of shift shock. 
In light of the foregoing, JP11 (1999)-69509A discloses a shift operation control apparatus for a hybrid-electric vehicle (HEV), on which an internal combustion engine and an electric motor are mounted as the driving power source.  The HEV further includes a multi-stage synchromesh-type transmission, in which a shift operation is automated, and a clutch device for automatically engaging and disengaging a clutch of a clutch assembly.  In this shift operation control apparatus, a loss of vehicle acceleration, i.e., the occurrence of vehicle deceleration, can be avoided by increasing a driving torque generated by an electric motor which is activated auxiliary while the clutch is in a state of disengagement.  The driving torque generated by the electric motor can be calculated on the basis of the depressing amount of an accelerator pedal, a variation of the depressing amount of the accelerator pedal and a driving torque from the engine after a shift operation.  The driving torque from the engine after the shift operation can be expected on the basis of an engine rotational speed prior to the shift operation.  The driving torque is thus generated by the electric motor on the basis of the engine driving torque after the shift operation, thereby making possible the gear ratio changing operation and an acceleration of the vehicle appropriate to an accelerator pedal operation performed by a vehicle driver. 
However, in the shift operation control apparatus described above, the driving torque generated by the electric motor at the time of a shift operation is generated, or intensified on the basis of a meet point of a clutch of the clutch assembly, a meet point which can be detected actually, or, alternatively on the basis of a clutch meet point which is predetermined.  The meet point can be defined as a point at which a vehicle starts moving from a vehicle stationary condition while the clutch is gradually engaged without an accelerator pedal operation.  Thus, it becomes possible to conceive in this shift operation control apparatus that a degree of shift shock is decreased, (1) by preventing any sudden cutting off of the driving torque from the engine to the transmission by detecting the clutch being partially engaged or by estimating a point where the clutch is partially engaged and (2) by generating an assist driving force by the electric motor. 
In this type of shift operation control apparatus, after a period of time in which the clutch has been partially disengaged at the time of a shift operation, the clutch is completely disengaged, a shift operation is performed in the transmission, and the clutch is again engaged.  To a driver who requires that a vehicle accelerates, such gear ratio changing operation including a shift operation in the transmission as well as a clutch engagement/disengagement operation appears to take longer than the actual period of time required for the gear ratio changing operation, thereby resulting in a feeling of a loss of vehicle acceleration. 
The present invention has been made in view of the above circumstances, and provides an apparatus for controlling a shift operation in a transmission, an apparatus which effectively reduces the degree of shift shock at the time of a gear ratio changing operation and also quickly achieves the gear ratio changing operation.