An endoscope adaptor for being connected to a robot arm of a robotic surgical system through a drape adaptor that puts a drape between the drape adaptor and the robot arm, comprising: a base section for being detachably connected to the drape adaptor ; a driven member that is rotatably provided on the base section and is configured to be rotated by a rotation drive section of the robot arm through the drape adaptor ; a holding section including a first holding member configured to hold an endoscope and includes a first gear formed on an outer circumference of the first holding member; and a second holding member that rotatably holds the first holding member and the holding section configured to hold the endoscope rotatably about a rotation axis, the endoscope including an insertion section including an image capturing section provided at a distal end of the insertion section and a body section connected to the insertion section , wherein the rotation axis extends in a direction (Y) in which the insertion section extends; and a transmission mechanism configured to transmit rotation of the driven member to the holding section configured to hold the endoscope , wherein the driven member includes a helical gear that rotates about a rotation axis in a direction (Z) crossing the direction (Y) in which the insertion section extends, and the transmission mechanism includes a cylindrical worm gear that meshes with the helical gear of the driven member and a second gear that is provided coaxially with the cylindrical worm gear and meshes with the first gear , such that the transmission mechanism rotates the first holding member of the holding section by rotation of the second gear . a base section for being detachably connected to the drape adaptor ; a driven member that is rotatably provided on the base section and is configured to be rotated by a rotation drive section of the robot arm through the drape adaptor ; a holding section including a first holding member configured to hold an endoscope and includes a first gear formed on an outer circumference of the first holding member; and a second holding member that rotatably holds the first holding member and the holding section configured to hold the endoscope rotatably about a rotation axis, the endoscope including an insertion section including an image capturing section provided at a distal end of the insertion section and a body section connected to the insertion section , wherein the rotation axis extends in a direction (Y) in which the insertion section extends; and a transmission mechanism configured to transmit rotation of the driven member to the holding section configured to hold the endoscope , wherein the driven member includes a helical gear that rotates about a rotation axis in a direction (Z) crossing the direction (Y) in which the insertion section extends, and the transmission mechanism includes a cylindrical worm gear that meshes with the helical gear of the driven member and a second gear that is provided coaxially with the cylindrical worm gear and meshes with the first gear , such that the transmission mechanism rotates the first holding member of the holding section by rotation of the second gear . <EOS>