Disclosed herein is a character input device for a mobile device or a wearable terminal. A bio radar unit senses the positions of the fingers of a user. A tilt sensor senses the tilt of the hands of the user. A microprocessor calculates the final input information of the user by processing signals received from the bio radar unit and the tilt sensor. A wireless communication module transmits the final input information to the mobile device or the wearable terminal of the user. A speaker device outputs a feedback sound corresponding to the final input information of the user. The character input device is wearable on a wrist of the user. The bio radar unit transmits a signal, measures the distance between the character input device and a finger by measuring the strength of a reflected wave reflected from the finger with which the signal collides, and measures the angle of the finger related to activation.