A data processing device includes a processor that executes a procedure. The procedure includes: (a) detecting a contact operation to a contacted face and receiving an instruction, (b) in a locked state, executing first determination to determine whether or not the contact operation detected at (a) is a pre-registered first contact operation, and executing second determination to determine whether or not a second contact operation to a different region from the region where the first contact operation has been detected has been performed, and (c) releasing the locked state when it is determined at (b) that the first contact operation and the second contact operation have been detected at (a).