The present invention provides an operation field-securing device 10 that secures an operation field 12 by being deployed within the body cavity 92. The operation field-securing device 10 includes at least three elongated parts 201 extending radially in a deployed state； and curved parts 202, the number of which is the same as that of the elongated parts 201. Each pair of the two adjacent elongated parts 201 is connected at their one ends by the curved part 202. Each of the curved parts 202 is convex toward a side opposite to the elongated part 201. In the deployed state, the curved parts 202 are arranged circumferentially. By deforming the curved parts 202, the operation field-securing device 10 is capable of being brought into either one of a contracted state where a distance between the adjacent elongated parts 201 is shortened by making the elongated parts 201 close to each other and the deployed state where the distance between the elongated parts 201 is expanded.
