A fuel vapor leak detecting apparatus, includes: a valve which is in a vapor purge system including a canister that is communicated with a fuel tank and an internal combustion engine, and which controllably closes the vapor purge system; a pressurizing section which introduces atmospheric air into the vapor purge system to pressurize the vapor purge system; and an internal-pressure measuring section which detects an internal pressure of the vapor purge system. The pressurizing section supplies the air for a predetermined time in a state where the vapor purge system is closed. When the internal pressure measured by the internal-pressure measuring section at the air supply is equal to or lower than a preset criterion pressure, it is judged that leak occurs.