1. A mobile radio terminal comprising: a key which has a fingerprint detecting function and operates to input an instruction in correspondence with a push position; a memory for registering a fingerprint detected by said key; a fingerprint collating portion for collating the fingerprint registered in said memory with a fingerprint which is newly detected by said key; and a switching portion for switching to allow the input of the instruction from said key only when it is judged through the fingerprint collation that the fingerprint newly detected is coincident with the fingerprint registered in the memory.