A wireless input device includes an information receiving terminal and an information outputting terminal. The information receiving terminal generates a first-portion key. The information outputting terminal receives the first-portion key and generating a second-portion key. An original information is converted into an encrypted information by the information outputting terminal according to the first-portion key, the second-portion key and an encryption algorithm. The encrypted information and the second-portion key are transmitted from the information outputting terminal to the information receiving terminal. The encrypted information is restored to the original information by the information receiving terminal according to the first-portion key, the second-portion key and an encryption algorithm.