A trocar comprising: a plate member which has at least one first through-hole formed therein for allowing a first surgical instrument to be inserted therethrough; at least one movable port which is provided separately from the plate member, is movable relative to the plate member, and has a second through-hole formed therein for allowing a second surgical instrument to be inserted therethrough; and a cylinder part which is provided at the plate member so as to communicate with an inside of the first through-hole and an inside of the second through-hole, and which is adapted to be attached to an incised wound, wherein the plate member has a guide hole part through which the movable port is inserted, wherein the guide hole part includes an elongated hole portion that allows the movable port to advance and retreat in a predetermined direction, wherein the elongated hole portion extends from a first end to a second end of the elongated hole portion in a longitudinal direction perpendicular to a central axis of the plate member, characterized in that the guide hole part further includes a locking portion that is configured to lock the movable port to a part of the guide hole part, wherein the locking portion is formed at an intermediate portion of the elongated hole portion between the first and the second end of the elongated hole portion in the longitudinal direction, wherein a sliding resistance in the longitudinal direction between the elongated hole portion and the movable port at both ends (7a, 7b) of the elongated hole portion is smaller compared to a sliding resistance in the longitudinal direction between the locking portion and the movable port. a plate member which has at least one first through-hole formed therein for allowing a first surgical instrument to be inserted therethrough; at least one movable port which is provided separately from the plate member, is movable relative to the plate member, and has a second through-hole formed therein for allowing a second surgical instrument to be inserted therethrough; and a cylinder part which is provided at the plate member so as to communicate with an inside of the first through-hole and an inside of the second through-hole, and which is adapted to be attached to an incised wound, wherein the plate member has a guide hole part through which the movable port is inserted, wherein the guide hole part includes an elongated hole portion that allows the movable port to advance and retreat in a predetermined direction, wherein the elongated hole portion extends from a first end to a second end of the elongated hole portion in a longitudinal direction perpendicular to a central axis of the plate member, characterized in that the guide hole part further includes a locking portion that is configured to lock the movable port to a part of the guide hole part, wherein the locking portion is formed at an intermediate portion of the elongated hole portion between the first and the second end of the elongated hole portion in the longitudinal direction, wherein a sliding resistance in the longitudinal direction between the elongated hole portion and the movable port at both ends (7a, 7b) of the elongated hole portion is smaller compared to a sliding resistance in the longitudinal direction between the locking portion and the movable port.