For charging in a non-contact manner, a mobile work robot is placed on a charging unit provided with a unit-side terminal providing an energy for charging. The mobile work robot receives an energy for charging the battery from the unit-side terminal via a robot-side terminal. For the charging, the mobile work robot is placed on the charging unit such that a surface provided with the robot-side terminal is opposed to a surface provided with the unit-side terminal. The surface portion provided with the robot-side terminal and the surface portion provided with the unit-side terminal form a protection unit, which is a space for cutting off a region for energy transmission for charging from an external side.