A gear shift control device for a hybrid vehicle drive system for controlling the hybrid vehicle drive system which comprises an automatic transmission including an input shaft configured to rotate by an engine torque (Te) which is outputted from an output shaft of an engine mounted to a vehicle and which is controlled by an output control mechanism (23, 28), and an output shaft rotatably connected to a driving wheel, the automatic transmission selectively engaging one of plural gear sets of a gear train by a gear switching mechanism (34, 35), the gear train allowing the input shaft and the output shaft to rotatably connect to each other with various gear ratios; a clutch configured to be operated between a connected state where the output shaft of the engine and the input shaft of the automatic transmission are rotatably connected to each other and a disconnected state where the output shaft and the input shaft are disconnected from each other; a clutch actuation mechanism adjusting a clutch torque (Tc) transmitted by the clutch to the input shaft of the automatic transmission; and a motor rotatably connected to the output shaft of the automatic transmission and the driving wheel, the motor generating a motor torque (Tm) which is addable to the engine torque (Te) and driving the driving wheel by the motor torque (Tm), the gear shift control device controlling the hybrid vehicle drive system to change a selection of the gear sets of the gear train of the automatic transmission, the gear shift control device comprising: a torque indication means for indicating a drive torque required for the driving wheel as a driver request torque (Tdrv) converted into the engine torque (Te), the drive torque being determined by an operation amount of an acceleration means operated by a driver; a gear shift control means for, when a gear shift condition is fulfilled, reducing the engine torque (Te) by the output control mechanism (23, 28) and driving the motor to generate the motor torque (Tm), for bringing the clutch in the disconnected state by the clutch actuation mechanism, for, after changing the selection of the gear sets of the gear train by the gear switching mechanism (34, 35), returning the clutch to the connected state by the clutch actuation mechanism, and for reducing the motor torque (Tm) and increasing the engine torque (Te); and a motor torque computing means for computing the motor torque (Tm) characterized in that said motor torque computing means computes the motor torque (Tm) on the basis of a first subtraction value during a period of time while a rotational difference (ΔN) obtained by subtracting a rotation speed (Ni) of the input shaft of the automatic transmission from a rotation speed (Ne) of the output shaft of the engine exceeds a first predetermined value after changing the selection of the gear sets of the gear train by the gear switching mechanism (34, 35) so as to increase the gear ratios, the first subtraction value being obtained by subtracting the clutch torque (Tc) from the driver request torque (Tdrv). a torque indication means for indicating a drive torque required for the driving wheel as a driver request torque (Tdrv) converted into the engine torque (Te), the drive torque being determined by an operation amount of an acceleration means operated by a driver; a gear shift control means for, when a gear shift condition is fulfilled, reducing the engine torque (Te) by the output control mechanism (23, 28) and driving the motor to generate the motor torque (Tm), for bringing the clutch in the disconnected state by the clutch actuation mechanism, for, after changing the selection of the gear sets of the gear train by the gear switching mechanism (34, 35), returning the clutch to the connected state by the clutch actuation mechanism, and for reducing the motor torque (Tm) and increasing the engine torque (Te); and a motor torque computing means for computing the motor torque (Tm) characterized in that said motor torque computing means computes the motor torque (Tm) on the basis of a first subtraction value during a period of time while a rotational difference (ΔN) obtained by subtracting a rotation speed (Ni) of the input shaft of the automatic transmission from a rotation speed (Ne) of the output shaft of the engine exceeds a first predetermined value after changing the selection of the gear sets of the gear train by the gear switching mechanism (34, 35) so as to increase the gear ratios, the first subtraction value being obtained by subtracting the clutch torque (Tc) from the driver request torque (Tdrv).