An operator cab for heavy construction equipment is disclosed to prevent a sliding door from rocking or rattling due to a shock or vibration applied to the cab in a state that the sliding door slidably mounted on the cab is opened or closed. The operator cab includes a sidewall member with a doorway, upper, central, and lower rails provided on upper, central, and lower portions of the sidewall member, respectively, a sliding door slid by upper, central, and lower rollers engaged with the upper, central, and lower rails, respectively, to open or close the doorway, upper and lower roller holders installed on ends of the upper and lower rails, respectively, in a shape corresponding to the upper and lower rollers, and having an engaging groove receiving and supporting the upper and lower rollers when the sliding door is fully opened or closed, a locking device having a pair of male and female locking strikers which are engaged to each other at one side of the sliding door when the slidingdoor is fully opened, and a locking holder formed on an external periphery of a loader corresponding to the male locking striker.