1. A work robot which executes a work to operate a target object, the work robot comprising: an image-capturing unit which captures an image including the target object; a storage unit which stores, during teaching, an image captured by the image-capturing unit and an operation content taught by an operator in correlation to each other; and a controlling unit which acquires, during work, an image captured by the image-capturing unit, searches the storage unit for an image which is similar to the acquired image, and operates the target object based on an operation content correlated to an image found from the storage unit as a result of the search; wherein the controlling unit creates information of a color included in an image captured by the image-capturing unit, and searches the storage unit for an image which is similar to the captured image by comparing information of a color difference between a pixel included in each image stored in the storage unit and a nearby pixel included in each image stored in the storage unit and the created information of a color difference between a pixel included in the captured image and a nearby pixel included in the captured image.