A pipe-forming apparatus (3J;3K;3L;3M) configured to form a spiral pipe by joining edges of a strip member adjacent with a difference of one lap with each other while spirally winding the strip member along a peripheral surface of an existing pipe, wherein the pipe-forming apparatus (3J;3K;3L;3M) comprises: an apparatus frame disposed on a partial part in a circumferential direction of a pipe end portion of a preceding spiral pipe portion configured to be formed in advance of the strip member, the pipe end portion configured to be provided on a forefront side in an extending direction along a pipe axis of the preceding spiral pipe portion, the apparatus frame having a propelling longitudinal direction being along a winding direction of the preceding spiral pipe portion; a driving part provided in the apparatus frame and configured to join the preceding spiral pipe portion with a following strip portion of the strip member following the preceding spiral pipe portion, the driving part obtaining a propelling force by pressing the following strip portion toward the preceding spiral pipe portion; characterized in that the pipe-forming apparatus (3J;3K;3L;3M) further comprises: a non-circular guide portion (63,73) provided so as to be rotatable with respect to the apparatus frame around a rotary axis (62,72) directed in a machine-width direction orthogonal to the propelling longitudinal direction, the non-circular guide portion (63,73) configured to be applied to a peripheral surface on a side of the preceding spiral pipe portion facing the existing pipe; and an acting portion (41;42;50;51) configured to act such that the non-circular guide portion (63,73) follows the peripheral surface of the existing pipe or the preceding spiral pipe portion, wherein the pipe-forming apparatus (3J;3K;3L;3M) is configured to perform pipe-forming in a state where a part of the pipe end portion other than the partial part is released from the pipe-forming apparatus (3J;3K;3L;3M). an apparatus frame disposed on a partial part in a circumferential direction of a pipe end portion of a preceding spiral pipe portion configured to be formed in advance of the strip member, the pipe end portion configured to be provided on a forefront side in an extending direction along a pipe axis of the preceding spiral pipe portion, the apparatus frame having a propelling longitudinal direction being along a winding direction of the preceding spiral pipe portion; a driving part provided in the apparatus frame and configured to join the preceding spiral pipe portion with a following strip portion of the strip member following the preceding spiral pipe portion, the driving part obtaining a propelling force by pressing the following strip portion toward the preceding spiral pipe portion; a non-circular guide portion (63,73) provided so as to be rotatable with respect to the apparatus frame around a rotary axis (62,72) directed in a machine-width direction orthogonal to the propelling longitudinal direction, the non-circular guide portion (63,73) configured to be applied to a peripheral surface on a side of the preceding spiral pipe portion facing the existing pipe; and an acting portion (41;42;50;51) configured to act such that the non-circular guide portion (63,73) follows the peripheral surface of the existing pipe or the preceding spiral pipe portion, wherein the pipe-forming apparatus (3J;3K;3L;3M) is configured to perform pipe-forming in a state where a part of the pipe end portion other than the partial part is released from the pipe-forming apparatus (3J;3K;3L;3M).