To provide a start control system capable of enhancing a security level and reliably preventing a start when illegal access is made to a driving medium for starting operation according to a key operation.

The start control system comprises a key medium 2 for storing an authentication code which changes according to the number of uses, a reading device 7 which reads the authentication code stored in the key medium 2, and modulates an output voltage of a battery 3 based on the read authentication code, and a collation device 8 which generates the authentication code by demodulating the voltage modulated by the reading device 7, executes collation processing by using the generated authentication code, and controls the start of an engine starter 4 based on the result of collation. The collation device 8 prohibits the start of the engine starter 4 when the authentication code other than a normal authentication code is inputted, a predetermined voltage is applied, or when the authentication code is inputted by a method other than a method for demodulating the output voltage of the battery 3.