To provide a user authenticating device which can eliminate the necessity for memorizing at all times the password symbol of a user of an information processor, etc., an also can eradicate a dangerous case where the password symbol is wrong used by another person.

A flash memory is built into a grip part 1B of a key 1 and stores previously information including the name, password symbol, etc., of a user which are necessary for the authentication of the user. Meanwhile, an information processor 2 also sets the same information as that including the name, password symbol, etc., of the user on an authentication means 2D. When the key 1 is put into a keyhole 2A, the information is read out of the flash memory and compared with the information set on the means 2D to authenticate a normal user.