A hydraulic oil tank attachment structure arranged in a construction machine secures the strength of a hydraulic oil tank as well as secures a large capacity thereof. The attachment structure is arranged in a compact excavator provided with a revolving superstructure, a working device attached to the revolving superstructure, a hydraulic actuator including a revolving motor that drives the revolving superstructure and an actuator that drives the working device. A hydraulic oil tank made of synthetic resin, which stores hydraulic oil to be supplied to the hydraulic actuator, is attached on a revolving frame of the revolving superstructure. The hydraulic oil tank attachment structure has a holding member provided with a projecting part formed on a side surface of the tank, which is fixed on the revolving frame of the revolving superstructure so as to surround side surfaces thereof to hold the hydraulic oil tank via the projecting part.