This invention provides a lens device and a correction method therefor whereby the focal position of the lens device can be corrected with high accuracy even if a lens surface shape or the like is not uniform. A ring-shaped lens fixing frame 52 is mounted on the outer periphery of a lens 51. A gear 53 is formed on the lens fixing frame 52 in the circumferential direction. A gear 54, which engages with the gear 53, is rotated by a motor 20A. Then, the lens 51 rotates about the optical axis L thereof. Further, a rack 57, which extends in the direction of the optical axis L, is formed on a part of the lens fixing frame 52. A pinion 58 engages with the teeth 57A of the rack 57, and the pinion 58 is rotated by another motor 20B. Then, the rack 57 moves in the direction of the optical axis L, and thus the lens 51 moves in the direction of the optical axis L. Since the lens 51 rotates about the optical axis L thereof, even if the surface shape or the like of the lens 51 is uneven in the circumferential direction, improvement can be realized.