US Patent 9836938 Shovel having audio output device installed in cab

A perimeter-monitoring device has a human presence determining part configured to determine presence or absence of a human in each of a plurality of monitoring spaces located around the shovel and an alarm controlling part configured to control a plurality of alarm output parts that are located in a cab of the shovel and emit an alarm to an operator. The alarm controlling part causes a right alarm output part to emit an alarm when it is determined that a human exists in a right monitoring space, causes a left alarm output part to emit an alarm when it is determined that a human exists in a left monitoring space, and causes a back alarm output part to emit an alarm when it is determined that a human exists in a back monitoring space.