A trace chip monitors a signal between a target logic chip having a data processing circuit mounted thereon and a memory chip having a memory storing data to be used by the target logic chip mounted therein, and traces an operation of the target logic chip. As the trace chip is implemented by a chip separate from the target logic chip and a memory chip, a debugging circuit need not be added to mass-produced articles when the trace chip is not mounted to the mass-produced articles. Thus, manufacturing cost of the articles can be reduced.