PURPOSE: To provide a back hoe which is designed to prevent a bucket from making contact with the external frame of an operation part even when a stop on a restraint surface is delayed.

CONSTITUTION: A back hoe is provided with a temperature sensor to detect the temperature of working oil for operating the hydraulic cylinder of a back hoe device 3 or an presence sensor to detect the presence of an excavated substance in a bucket 6. When the temperature of working oil is lowered below a set temperature or when an excavated substance is present in the bucket 6, the position of a retraint surface A1 is spaced further externally away from external frames 29 and 30 of an operation part.