A bending joint mechanism comprising a first joint section (3, 194), the first joint section (3, 194) comprising: a first shaft section (2, 192) which has an arc-shaped first rotation guide portion (8, 198) around a first rotation center (O1, O11) and which has an axis that intersects at right angles with the axis of the first rotation center (O1, O11), wherein the first shaft section (2, 192) has a cylindrical housing (12, 204), and wherein a rod receiver is fixed in the housing (12, 204); a first actuating section (6, 196) having an arc-shaped second rotation guide portion (9, 199) around a second rotation center (02, O12), the second rotation guide portion (9, 199) being configured to come in rolling contact with the first rotation guide portion (8, 198) at a proximal end portion thereof; a first coupling member (7, 206) which is rotatably coupled at a distal end portion thereof to the second rotation center (02, O12) and which is rotatably coupled at a proximal end portion thereof to the first rotation center (01, O11); and a first rod section (13, 205) supported translatably, by the rod receiver, relative to the first shaft section (2, 192) in the axial direction of the shaft section (2, 192) and which is coupled at a distal end portion thereof to a position other than the first rotation center (O1, O11) of the coupling member (7, 206) and which is configured to translate, under the guidance of the rod receiver, in the axial direction of the first shaft section (2, 192) in response to a driving force transmitted from a driving source, wherein the bending joint mechanism is configured to turn the second rotation guide portion (9, 199) around the first rotation center (O1, O11) along the first rotation guide portion (8, 198) via the first coupling member (7, 206) together with the translating of the first rod section (13, 205) to bend the first actuating section (6, 196) relative to the first shaft section (2, 192), and the first rod section (13, 205) has an elastic portion (16, 205) which is elastically deformable in directions other than the axial direction of the first shaft section (2, 192). a first shaft section (2, 192) which has an arc-shaped first rotation guide portion (8, 198) around a first rotation center (O1, O11) and which has an axis that intersects at right angles with the axis of the first rotation center (O1, O11), wherein the first shaft section (2, 192) has a cylindrical housing (12, 204), and wherein a rod receiver is fixed in the housing (12, 204); a first actuating section (6, 196) having an arc-shaped second rotation guide portion (9, 199) around a second rotation center (02, O12), the second rotation guide portion (9, 199) being configured to come in rolling contact with the first rotation guide portion (8, 198) at a proximal end portion thereof; a first coupling member (7, 206) which is rotatably coupled at a distal end portion thereof to the second rotation center (02, O12) and which is rotatably coupled at a proximal end portion thereof to the first rotation center (01, O11); and a first rod section (13, 205) supported translatably, by the rod receiver, relative to the first shaft section (2, 192) in the axial direction of the shaft section (2, 192) and which is coupled at a distal end portion thereof to a position other than the first rotation center (O1, O11) of the coupling member (7, 206) and which is configured to translate, under the guidance of the rod receiver, in the axial direction of the first shaft section (2, 192) in response to a driving force transmitted from a driving source, wherein the bending joint mechanism is configured to turn the second rotation guide portion (9, 199) around the first rotation center (O1, O11) along the first rotation guide portion (8, 198) via the first coupling member (7, 206) together with the translating of the first rod section (13, 205) to bend the first actuating section (6, 196) relative to the first shaft section (2, 192), and the first rod section (13, 205) has an elastic portion (16, 205) which is elastically deformable in directions other than the axial direction of the first shaft section (2, 192).