A method and apparatus for centering a log allow a optimum yield axis and a maximum radius of rotation of the log to be calculated more accurately than conventionally possible. The angle of rotation of a log M is detected by a rotation angle detector 6 that is engaged with a preliminary axis c about which the log M is rotated. A contour of the log for calculating the optimum yield axi s of the log and a contour for calculating the maximum radius of rotation of the log are measured separately. The contour for calculating the optimum yield axis is measured in a fixed-point manner by measuring the log at a plurality of certain measurement points with beam reflection scanners 8 disposed at appropriate intervals along the axis of the log M. The contour for calculating the maxim um radius of rotation is measured in a comprehensive manner by measuring the lo g in a plurality of measurement sections allocated on the log along the axis thereof with virtually no gap therebetween, using swing-angle detectors 15 engaged with contact-swinging detection members provided individually in the plural measurement sections.
