We developed a three-dimensional position sensor that can measure the position of a capsule in the digestive tract. For the purpose of inspecting a new position measurement algorithm, we first developed a prototype wired capsule-type sensor that is capable of being swallowed. Our ultimate goal will be to develop a wireless sensor. The current sensor is applicable for medical capsule devices, such as capsule endoscope. The position of the sensor was detected using mutual induction. In order to maintain the electromotive force induced at secondary coils in the sensor constant, the current flowing into the primary coil was regulated using feedback control. The position of the sensor was measured stably using the feedback control, even when the sensor was relatively far from the primary coil. The position of the sensor was determined from the current flowing into the primary coil. As a result of evaluating the accuracy of the wired sensor in vitro, the error was 2.90 ± 2.10 mm (Ave.± S. D.) in a range of up to 1m from the magnetic field generator. Moreover, using a new position compensation algorithm, we were able to remove distortion caused by the magnetic field.