1. A vibration testing device comprising one or more actuator systems each including an actuator having a movable part for applying a deformation to a test piece, a control sensor for measuring a drive condition of the actuator, an actuator controlling device for controlling the drive condition of the actuator by using an input instruction signal and an output of the control sensor, and a monitoring sensor for measuring the response condition of the test piece and the drive condition of the actuator; and a computer system for outputting an instruction signal to each actuator system, wherein the computer system has: a measurement processing block for inputting an output of the monitoring sensor and processing the output to be used in a parameter changing block; a model substituting block for modeling characteristics of the test piece excited in the actuator system by using a finite number of parameters, calculating a response quantity corresponding to the drive condition of the actuator, and inputting the calculation result to a numerical simulation block and the parameter changing block; the parameter changing block for comparing the calculation result of the model substituting block with the processing result of the measurement processing block, and changing the parameter such that the actual characteristics of the test piece substantially coincides with the characteristics of the test piece in the model substituting block; the numerical simulation block for calculating a vibration response at each interval of a preset time in accordance with a previously input structure numerical model, the processing result of the model substituting block, and a time function given as an external force applied to the structure; and a waveform generating block for calculating a time function of a deformation to be applied to the test piece in accordance with the result of the numerical simulation block, and outputting it as an instruction value to the actuator controlling device, repeatedly performing a series of processes of the model substitution, the numerical simulation and the waveform generation, and a series of processes of the measurement processing and the parameter change in parallel.