A component mounting line comprising: multiple component mounters arranged in a row along a conveyance direction of a circuit board, the component mounters being configured to mount components supplied from feeders set on a feeder setting section of each of the component mounters on the circuit board; an automatic exchanging device configured to move along a moving lane provided along the row of the multiple component mounters, and to set and remove the feeders to and from the feeder setting section of each of the component mounters; a driving device configured to drive the automatic exchanging device along the moving lane using a driving wheel; a position detecting device configured to detect the position of the automatic exchanging device; and a control device configured to move the automatic exchanging device to a specified position using the driving device based on a detection result of the position detecting device, characterized in that the position detecting device includes a timing belt with an end provided to extend in a straight line along the moving lane straddling the multiple component mounters, a timing pulley configured to move together with the automatic exchanging device while maintaining a state of being engaged with teeth of the timing belt, a rotation angle sensor configured to detect a rotation angle of the timing pulley, a detecting circuit section configured to detect a position of the automatic exchanging device based on an output signal of the rotation angle sensor, a support mechanism configured to variably change a position of the timing pulley in a direction perpendicular to that of the timing belt within a range in which the teeth of the timing pulley and the teeth of the timing belt remain engaged, and a biasing means configured to bias the timing pulley in a direction pushed towards the timing belt. multiple component mounters arranged in a row along a conveyance direction of a circuit board, the component mounters being configured to mount components supplied from feeders set on a feeder setting section of each of the component mounters on the circuit board; an automatic exchanging device configured to move along a moving lane provided along the row of the multiple component mounters, and to set and remove the feeders to and from the feeder setting section of each of the component mounters; a driving device configured to drive the automatic exchanging device along the moving lane using a driving wheel; a position detecting device configured to detect the position of the automatic exchanging device; and a control device configured to move the automatic exchanging device to a specified position using the driving device based on a detection result of the position detecting device, characterized in that the position detecting device includes a timing belt with an end provided to extend in a straight line along the moving lane straddling the multiple component mounters, a timing pulley configured to move together with the automatic exchanging device while maintaining a state of being engaged with teeth of the timing belt, a rotation angle sensor configured to detect a rotation angle of the timing pulley, a detecting circuit section configured to detect a position of the automatic exchanging device based on an output signal of the rotation angle sensor, a support mechanism configured to variably change a position of the timing pulley in a direction perpendicular to that of the timing belt within a range in which the teeth of the timing pulley and the teeth of the timing belt remain engaged, and a biasing means configured to bias the timing pulley in a direction pushed towards the timing belt. a timing belt with an end provided to extend in a straight line along the moving lane straddling the multiple component mounters, a timing pulley configured to move together with the automatic exchanging device while maintaining a state of being engaged with teeth of the timing belt, a rotation angle sensor configured to detect a rotation angle of the timing pulley, a detecting circuit section configured to detect a position of the automatic exchanging device based on an output signal of the rotation angle sensor, a support mechanism configured to variably change a position of the timing pulley in a direction perpendicular to that of the timing belt within a range in which the teeth of the timing pulley and the teeth of the timing belt remain engaged, and a biasing means configured to bias the timing pulley in a direction pushed towards the timing belt.