To execute a stable pressure control, in a control device for an injection molding machine, a filling/pressure-keeping determining unit determines whether the injection molding machine is performing a pressure keeping operation, an elastic constant identifier acquires, when the filling/pressure-keeping determining unit determines that the pressure keeping operation is in progress, a pressure detection value and a position detection value as operation information of a motor and identifies an elastic constant K based on the acquired pressure detection value and the position detection value, and a pressure-control control-parameter setting unit calculates a proportional gain Ka of a pressure controller such that a product of the proportional gain Ka of the pressure controller and the elastic constant K is smaller than a speed control bandwidth ωsc of a speed controller, and sets the calculated proportional gain Ka to the pressure controller.