The invention discloses a welded pipe end straightness online detection device, belonging to the technical field of welding control, and comprising a detection mechanism, a detection arm, a pedestal mechanism and a base mechanism, wherein the pedestal mechanism is arranged at the upper part of the base mechanism, the detection arm is arranged at the side surface of the pedestal mechanism, the two ends of the detection arm are respectively connected with the detection mechanism and the pedestal mechanism, the detection mechanism is positioned right above a welded pipe to be detected, and the detection mechanism, the detection arm and the pedestal mechanism are all positioned at the same side of the base mechanism. The invention is the online detection device which can substitute a manual visual inspection method to detect, and realize end straightness online automatic detection of welded pipes with different specifications.