Embodiments of the present invention provide a microcomputer on which a plurality of ICs (Integrated Circuits) connected from one another by a source-synchronous interface is mounted. The microcomputer includes an IC on the side for transmitting data through the source-synchronous interface which further includes: a PLL (Phase-Locked Loop) circuit being adapted for transmitting an operation clock in actual operation; a first flip-flop being adapted for transmitting test data in accordance with the operation clock transmitted from the PLL circuit; and a second flip-flop being adapted for transmitting a synchronous clock in source-synchronous, in accordance with the operation clock transmitted from the PLL circuit, a synchronous clock in source synchronous, and an IC on the side for receiving data through the source-synchronous interface which further includes a third flip-flop being adapted for capturing, in accordance with the synchronous clock transmitted from the second flip-flop, the test data transmitted from the first flip-flop. Methods for testing the microcomputer are also provided.