A dancer roller apparatus, comprising: a dancer roller (15a, 15b) which is arranged with a gap on a conveying path of a long object to convey the long object and is provided between a downstream side conveying unit and an upstream side conveying unit to absorb an amount of slack of the long object between the upstream side conveying unit and the downstream side conveying unit and provide tension to the long object; a drive motor for changing a position of the dancer roller (15a, 15b) during conveying of the long object and at a time of loading to switch a path length of the long object; and a dancer roller position changing unit which transmits a driving force from the drive motor to change the position of the dancer roller (15a, 15b), wherein the dancer roller position changing unit is provided with a one way clutch which allows the dancer roller (15a, 15b) to move in a long object slack direction, and wherein the drive motor is caused to rotate in a direction such that the dancer roller (15a, 15b) moves the one way clutch in a long object stretching direction during the conveying of the long object, characterized by further comprising a speed setting and inputting unit for setting a rotational speed of the drive motor, wherein the speed setting and inputting unit is configured to calculate a position moving speed of the dancer roller (15a, 15b) based on a difference in a long object conveying speed of the upstream side conveying unit and the downstream side conveying unit during the long object conveying to determine a rotational speed of the drive motor in accordance with the calculated value. a dancer roller (15a, 15b) which is arranged with a gap on a conveying path of a long object to convey the long object and is provided between a downstream side conveying unit and an upstream side conveying unit to absorb an amount of slack of the long object between the upstream side conveying unit and the downstream side conveying unit and provide tension to the long object; a drive motor for changing a position of the dancer roller (15a, 15b) during conveying of the long object and at a time of loading to switch a path length of the long object; and a dancer roller position changing unit which transmits a driving force from the drive motor to change the position of the dancer roller (15a, 15b), wherein the dancer roller position changing unit is provided with a one way clutch which allows the dancer roller (15a, 15b) to move in a long object slack direction, and wherein the drive motor is caused to rotate in a direction such that the dancer roller (15a, 15b) moves the one way clutch in a long object stretching direction during the conveying of the long object, characterized by further comprising a speed setting and inputting unit for setting a rotational speed of the drive motor, wherein the speed setting and inputting unit is configured to calculate a position moving speed of the dancer roller (15a, 15b) based on a difference in a long object conveying speed of the upstream side conveying unit and the downstream side conveying unit during the long object conveying to determine a rotational speed of the drive motor in accordance with the calculated value.