Disclosed is a storage medium with built-in antenna comprising a circuit board (12) on which a semiconductor device (15) is mounted, first and second magnetic layers (40, 42) sandwiching the semiconductor device (15) and the circuit board (12), and first and second antenna coils (25, 31) respectively arranged on the first and second magnetic layers (40, 42). The first and second antenna coils (25, 31) are connected in parallel on a flexible sheet, and the first and second antenna coils (25, 31) are respectively folded toward the first and second magnetic layers (40, 42) and electrically connected to the semiconductor device (15).