A device for supplying a tire-constituting member which supplies the tire-constituting member to a front side of a molding drum, comprising: a placement portion to which the tire-constituting member is supplied from the rear side so as to be placed on the placement portion; a first holding means which is disposed so as to hold a front end portion of the tire-constituting member and is disposed so as to be movable; and a second holding means which is disposed so as to hold a rear end portion of the tire-constituting member cut to a predetermined length and is disposed so as to be movable; wherein the first and second holding means (12, 13) are configured to hold the tire-constituting member that is cut to the predetermined length and is positioned on the placement portion, and the first and second holding means (12, 13) are configured to supply the tire-constituting member to the front side, the device further comprising: a detection means configured to detect positions of two corner portions (W3, W4) of the front end portion placed on the placement portion; and a control unit configured to calculate a deviation amount (A1, A2, A3, A4) of the two corner portions (W3, W4) of the front end portion with respect to two preset reference positions (K1, K2) of the two corner portions (W3, W4) of the front end portion according to data from the detection means and configured to drive the first holding means in a state where the rear end portion is held by the second holding means such that the two corner portions (W3, W4) of the front end portion are positioned at the two reference positions (K1, K2) of the two corner portions (K1, K2) of the front end portion so as to eliminate the deviation amount (A1, A2, A3, A4) of the two corner portions (K1, K2) of the front end portion according to the calculation results. a placement portion to which the tire-constituting member is supplied from the rear side so as to be placed on the placement portion; a first holding means which is disposed so as to hold a front end portion of the tire-constituting member and is disposed so as to be movable; and a second holding means which is disposed so as to hold a rear end portion of the tire-constituting member cut to a predetermined length and is disposed so as to be movable; wherein the first and second holding means (12, 13) are configured to hold the tire-constituting member that is cut to the predetermined length and is positioned on the placement portion, and the first and second holding means (12, 13) are configured to supply the tire-constituting member to the front side, the device further comprising: a detection means configured to detect positions of two corner portions (W3, W4) of the front end portion placed on the placement portion; and a control unit configured to calculate a deviation amount (A1, A2, A3, A4) of the two corner portions (W3, W4) of the front end portion with respect to two preset reference positions (K1, K2) of the two corner portions (W3, W4) of the front end portion according to data from the detection means and configured to drive the first holding means in a state where the rear end portion is held by the second holding means such that the two corner portions (W3, W4) of the front end portion are positioned at the two reference positions (K1, K2) of the two corner portions (K1, K2) of the front end portion so as to eliminate the deviation amount (A1, A2, A3, A4) of the two corner portions (K1, K2) of the front end portion according to the calculation results. a detection means configured to detect positions of two corner portions (W3, W4) of the front end portion placed on the placement portion; and a control unit configured to calculate a deviation amount (A1, A2, A3, A4) of the two corner portions (W3, W4) of the front end portion with respect to two preset reference positions (K1, K2) of the two corner portions (W3, W4) of the front end portion according to data from the detection means and configured to drive the first holding means in a state where the rear end portion is held by the second holding means such that the two corner portions (W3, W4) of the front end portion are positioned at the two reference positions (K1, K2) of the two corner portions (K1, K2) of the front end portion so as to eliminate the deviation amount (A1, A2, A3, A4) of the two corner portions (K1, K2) of the front end portion according to the calculation results.