1. A control device for an internal combustion engine with a turbocharger including a throttle that is disposed in an intake passage, a variable valve timing mechanism that changes a valve timing of an intake valve, and a waste gate valve, the control device comprising: target intake air amount determining means that determines a target intake air amount in a predetermined time step; intake pipe pressure limit change amount calculating means that calculates, by use of a relational expression established between a throttle flow rate being a flow rate of air passing through the throttle, an intake valve flow rate being a flow rate of air passing through an intake valve, and an amount of change in an intake pipe pressure and a relational expression established between an opening of the throttle and a throttle flow rate, a maximum amount of increase in an intake pipe pressure in the predetermined time step achieved by manipulating the throttle to an opening side at a maximum speed and a maximum amount of decrease in an intake pipe pressure in the predetermined time step achieved by manipulating the throttle to an closing side at a maximum speed from a current intake pipe pressure and a current intake valve flow rate; actuator command value determining means that determines, by use of a relational expression established between an intake pipe pressure, an intake valve flow rate, and respective operating states of the variable valve timing mechanism and the waste gate valve and a relational expression established between an intake valve flow rate and an intake air amount, a command value for each of the variable valve timing mechanism and the waste gate valve sb that an amount of change in an intake pipe pressure in the predetermined time step required to achieve the target intake air amount falls within a range from the maximum amount of decrease to the maximum amount of increase; and target throttle opening calculating means that calculates a target opening for the throttle for a purpose of achieving the target intake air amount under the determined actuator command value.