VEHICULAR POSITION ESTIMATION SYSTEM

A vehicular position estimation system determines a portable terminal position by causing multiple in-vehicle communication devices placed at different positions on a vehicle to wirelessly communicate with a potable terminal, and includes: a distance index value acquisition portion that acquires a distance index value indicating a distance between the multiple in-vehicle communication devices; a normal range storage portion that stores data indicating a normal range of the distance index value; and a communication device diagnosis portion that determines whether the in-vehicle communication device is normal. When the distance index value between a diagnosis target device and at least one different device is in a normal range, the communication device diagnosis portion determines that a failure does not occur in the diagnosis target device.