A capsule medical device (10) includes an LC resonance circuit (111) that generates a resonance magnetic field having a resonance frequency in accordance with an input induction signal or a drive magnetic field generated in a detection space (K) and a first dwitch (SW1, FIG. 2 ) that connects/disconnects between the LC resonance circuit (111) and other lines. An external apparatus (200) includes drive coils (223a, 223b) that generate a drive magnetic field in the detection space (K) in accordance with a frive signal and a second switch (SW2) that electrically disconnects the drive coils (223a, 223b). The second switch (SW2) is turned on when the first switch (SW1) is off. The second switch (SW2) is turned off when the first switch (SW1) is on. The LC resonance circuit (111) generates a resonance magnetic field in accordance with the induction signal or the drive magnetic field.
