A lay-up-position correcting method for an automatic lay-up machine including a head device including a sheet supplying unit in which a raw-cloth roller having a long prepreg sheet wound therearound is mounted and that supplies the prepreg sheet from the raw-cloth roller, the prepreg sheet including sheet-shaped prepreg and release paper bonded to a surface of the prepreg, a lay-up unit that lays up the prepreg on a receiving surface by pressing the prepreg sheet supplied by the sheet supplying unit against the receiving surface with a lay-up head, and a sheet take-up unit that takes up the release paper separated from the prepreg when the prepreg is laid up, and a support mechanism that supports the head device and includes a mechanism for moving the head device at least in a lay-up direction of the prepreg and a width direction of the prepreg sheet, wherein the lay-up-position correcting method corrects a position of the prepreg sheet in the width direction at a start of a lay-up operation performed by the automatic lay-up machine, and wherein the lay-up-position correcting method comprises: a first step of establishing a state in which a position of the raw-cloth roller coincides with a lay-up position in the width direction by moving the head device to a starting point of the lay-up position while the head device is in a state in which an end portion of the prepreg sheet fed from the raw-cloth roller is below the lay-up head and in which a predetermined tension is applied to the prepreg sheet; a second step of determining a deviation between a position of an edge of the prepreg sheet and the lay-up position in the width direction; a third step of establishing a state in which the position of the edge of the prepreg sheet coincides with the lay-up position in the width direction by moving the head device by a movement amount corresponding to the deviation in a movement direction along the width direction for cancelling the deviation; a fourth step of establishing a state in which the end portion of the prepreg sheet is pressed against the receiving surface at the starting point of the lay-up position by moving the head device or the lay-up head downward; and a fifth step of reestablishing the state in which the position of the raw-cloth roller coincides with the lay-up position in the width direction by moving the head device in a direction along the width direction opposite to the movement direction in the third step by an amount equal to the movement amount in the third step. a sheet supplying unit in which a raw-cloth roller having a long prepreg sheet wound therearound is mounted and that supplies the prepreg sheet from the raw-cloth roller, the prepreg sheet including sheet-shaped prepreg and release paper bonded to a surface of the prepreg, a lay-up unit that lays up the prepreg on a receiving surface by pressing the prepreg sheet supplied by the sheet supplying unit against the receiving surface with a lay-up head, and a sheet take-up unit that takes up the release paper separated from the prepreg when the prepreg is laid up, and a first step of establishing a state in which a position of the raw-cloth roller coincides with a lay-up position in the width direction by moving the head device to a starting point of the lay-up position while the head device is in a state in which an end portion of the prepreg sheet fed from the raw-cloth roller is below the lay-up head and in which a predetermined tension is applied to the prepreg sheet; a second step of determining a deviation between a position of an edge of the prepreg sheet and the lay-up position in the width direction; a third step of establishing a state in which the position of the edge of the prepreg sheet coincides with the lay-up position in the width direction by moving the head device by a movement amount corresponding to the deviation in a movement direction along the width direction for cancelling the deviation; a fourth step of establishing a state in which the end portion of the prepreg sheet is pressed against the receiving surface at the starting point of the lay-up position by moving the head device or the lay-up head downward; and a fifth step of reestablishing the state in which the position of the raw-cloth roller coincides with the lay-up position in the width direction by moving the head device in a direction along the width direction opposite to the movement direction in the third step by an amount equal to the movement amount in the third step.