To make full automation without mannual operation, by providing a control box for starting a self-traveling vehicle on the basis of a signal after a work is loaded on an empty truck in a work loading place on a self-traveling vehicle waiting place.

A control box 1 is provided near a self-traveling vehicle waiting place 100. A self-traveling vehicle A is started from the self-traveling vehicle waiting place 100 on the basis of a signal based on the control box 1. A microcomputer is built in the control box 1, so constituted as to transmit a signal to the self-traveling vehicle A when a signal after a work is loaded on an empty truck B by a robot 21 in a work loading place 20 is input. At the same time that the signal is input by the control box 1, the signal is transmitted to an empty truck supplying mechanism 10, the empty truck B is automatically supplied from the empty truck supplying mechanism 10 to the empty truck connecting place.