1. A drive control device of a hybrid vehicle that controls driving of the vehicle using outputs of an internal combustion engine and a plurality of motor generators, the drive control device comprising: an accelerator opening degree detecting means that detects the accelerator opening degree; a vehicle speed detecting means that detects a vehicle speed; a battery charge state detecting means that detects a charge state of a battery; a target driving power setting means that sets target driving power based on the accelerator opening degree that is detected by the accelerator opening degree detecting means and the vehicle speed detected by the vehicle speed detecting means; a target charge/discharge power setting means that sets target charge/discharge power based on at least the charge state of the battery that is detected by the battery charge state detecting means; a target engine power calculating means that calculates target engine power from the target driving power setting means and the target charge/discharge power setting means; a target engine operating point setting means that sets a target engine operating point based on the target engine power and total system efficiency; and a motor torque instruction value calculating means that sets torque instruction values of the plurality of motor generators, wherein the target driving power setting means sets driving power corresponding to a state in which power assistance depending on electric power of the battery is received as a maximal value of the target driving power in advance, wherein the target engine power calculating means sets a maximal value of the target engine power corresponding to a maximal output that can be output by the internal combustion engine in advance, compares the target engine power and the maximal value of the target engine power calculated by the target driving power setting means and the target charge/discharge power setting means with each other, and updates the target engine power with a smaller value thereof, wherein a target electric power calculating means calculating target electric power that is a target value of input/output electric power for the battery based on a difference between the target driving power and the target engine power is arranged, and wherein the motor torque instruction value calculating means calculates torque instruction values of the plurality of motor generators by using a torque balance equation including target engine torque required at the target engine operating point and an electric power balance equation including the target electric power.