Optical apparatus that is easy to assemble, and prevents occurrence of assembling failure

An optical apparatus that includes an operation ring part having at least a first operation ring and a second operation ring, which are arranged along a predetermined axis, and are rotatable about the predetermined axis, comprising:

• a first detection section that detects rotation of the first operation ring;
• a second detection section that detects rotation of the second operation ring;
• a transmission mechanism that is moved in accordance with rotation of the second operation ring, and transmits rotation of the second operation ring to the second detection section;
• and
• a regulation member that regulates a range of rotation of the second operation ring to a predetermined angle range,
• wherein when assembling the operation ring part, the first detection section and the second detection section are inserted from the same direction, and the first detection section is disposed in an angle range excluding an angle range through which the transmission mechanism is moved when the second operation ring is rotated through the predetermined angle range,
• wherein the transmission mechanism includes a first gear which is provided on the second operation ring, and a second gear which is provided on the second detection section, and is meshed with the first gear, and
• wherein the first detection section is arranged in a range where the first gear does not pass.