Provided are a method for discerning the cause of mounting displacement and a device for mounting electronic circuit components that have superior practicality. A circuit board on which electronic circuit components are mounted is imaged and inspected; when mounting displacements that exceed a permissible range occur in a set number or greater, causes are discerned. After a component (112) is held in a suction nozzle (104) and imaged by a lower side component imaging device (180), the same is moved to a board holding device by a set movement pattern; after moving, the same is returned so as to be above the lower side component imaging device (180) by a movement pattern that assures that movement of the component (112) with respect to the suction surface (110) does not occur and imaged. If the difference in the held position error is large before and after the movement, displacement during linear transverse movement is judged to be at least one cause of mounting displacement. Judgment is also made as to whethe
