The present invention provides an optical fiber which has a hollow portion extending along the axis and which reduces degradation of the optical characteristics, and a production method thereof. The regression coefficient calculation unit further calculates the regression coefficient using only the pixels classified as the first discrimination class and further calculates the regression coefficient using only the pixel classified as the second discrimination class. The main control unit determines whether the tool is changed on the basis of at least either of the exchange history and the update history. The internal surface of the neck engages with a fitment inserted into the neck of the plastic container to prevent movement of the fitment.