A platform performs wireless power supply to an underwater mobile object having a relatively movable relationship using coil pairs disposed to be opposable. The platform includes: a recessed section configured to accommodate at least a part of the underwater mobile object with a gap; a coil configured to constitute the first opposable coil pair (5A) on a first wall portion of the recessed section facing each other; and a coil configured to constitute the second opposable coil pair on a second wall portion of the recessed section facing each other.