To mainly automatically separate a carriage, without using an exclusive power source.

The present invention relates to a coupling device of an unmanned carrier 1 for connecting the carriage 3 by a coupling apparatus 2 installed in a rear part of the unmanned carrier 1. The coupling apparatus 2 comprises an upper plate 12 and a lower plate 13 suspended-supported from the unmanned carrier 1. In a state where a surface of turning to the rear of the upper plate 12 and a surface of turning to the rear of the lower plate 13 have an angle 15 smaller than 180 degrees, the other side part of the lower plate 13 is grounded on a rear position more than a fitting position to a rear part of the unmanned carrier 1 of the upper plate 12. An upward hook part 14 is also provided so that a carriage 3 can be locked from the lower side by being liftably moved by tilting of the upper plate 12.