There is provided a keyless entry system in which a permanent code, or first code, and a user's code, or second code are used. The second code is presettable in conjunction with use of the first code. When the first code is inputted, the system gets ready for presetting a desired number of code elements consituting the second code. According to the invention, the system is provided with a circuit for variably presetting the number of the code elements, which circuit is responsive to the first code to vary the presetted number of the second code elements to that inputted following to the input of the first code. Preferably, the keyless entry system further includes a theft prevention circuit which inhibits input of a code for a given period of time when wrong codes are inputted more than a predetermined number of times.