A test device that makes a test of a circuit device including a plurality of modules being substitutable in terms of function for one another, and in which a function change can be made for assignment to each of the modules based on an incoming control signal. The test device includes: a control section that generates the control signal, without changing a function to be assigned to a whole of the modules, to make the function change for assignment to each of the modules at least in a group of the modules; and a determination section that detects whether the circuit device operates differently when the function change is made for assignment to the modules, and based on a detection result, determines whether or not at least the group of the modules includes a defective module.