A method of calibrating a gear measuring device having: a measuring instrument that outputs a position signal indicating a position at which a gauge head is in contact with a measurement gear when the gauge head is brought into contact with a tooth surface of the measurement gear and that is driven along directions of three-dimensional directions; and an arithmetic means that carries out measurement of the measurement gear by subjecting the position signal to arithmetic processing; the method comprising: a step of obtaining a tooth profile of the measurement gear by subjecting the position signal to arithmetic processing and of obtaining a tooth profile gradient error (α1) of the measurement gear from the tooth profile, the position signal output when the gauge head is brought into contact with a tooth surface of the measurement gear when the measurement gear is rotated about a rotational axis thereof in synchronization with movement of the gauge head in a tangential direction of a base circle; a step of obtaining a tooth profile of the measurement gear by subjecting the position signal to arithmetic processing and of obtaining a tooth profile gradient error (α2) of the measurement gear from the tooth profile, the position signal output when the gauge head is brought into contact with the tooth surface of the measurement gear when the measurement gear is rotated about the rotational axis thereof in synchronization with movement of the gauge head in a direction other than the tangential direction of the base circle; a step of calculating a difference (Δα) between the tooth profile gradient errors that is a difference between the tooth profile gradient error (α1) and the tooth profile gradient error (α2); a step of obtaining a position error (Δx) of the gauge head by using the difference (Δα) between the tooth profile gradient errors and using a gear specification of the measurement gear; and a step of calibrating the position of the gauge head based on the position error (Δx). a measuring instrument that outputs a position signal indicating a position at which a gauge head is in contact with a measurement gear when the gauge head is brought into contact with a tooth surface of the measurement gear and that is driven along directions of three-dimensional directions; and an arithmetic means that carries out measurement of the measurement gear by subjecting the position signal to arithmetic processing; the method comprising: a step of obtaining a tooth profile of the measurement gear by subjecting the position signal to arithmetic processing and of obtaining a tooth profile gradient error (α1) of the measurement gear from the tooth profile, the position signal output when the gauge head is brought into contact with a tooth surface of the measurement gear when the measurement gear is rotated about a rotational axis thereof in synchronization with movement of the gauge head in a tangential direction of a base circle; a step of obtaining a tooth profile of the measurement gear by subjecting the position signal to arithmetic processing and of obtaining a tooth profile gradient error (α2) of the measurement gear from the tooth profile, the position signal output when the gauge head is brought into contact with the tooth surface of the measurement gear when the measurement gear is rotated about the rotational axis thereof in synchronization with movement of the gauge head in a direction other than the tangential direction of the base circle; a step of calculating a difference (Δα) between the tooth profile gradient errors that is a difference between the tooth profile gradient error (α1) and the tooth profile gradient error (α2); a step of obtaining a position error (Δx) of the gauge head by using the difference (Δα) between the tooth profile gradient errors and using a gear specification of the measurement gear; and a step of calibrating the position of the gauge head based on the position error (Δx). a step of obtaining a tooth profile of the measurement gear by subjecting the position signal to arithmetic processing and of obtaining a tooth profile gradient error (α1) of the measurement gear from the tooth profile, the position signal output when the gauge head is brought into contact with a tooth surface of the measurement gear when the measurement gear is rotated about a rotational axis thereof in synchronization with movement of the gauge head in a tangential direction of a base circle; a step of obtaining a tooth profile of the measurement gear by subjecting the position signal to arithmetic processing and of obtaining a tooth profile gradient error (α2) of the measurement gear from the tooth profile, the position signal output when the gauge head is brought into contact with the tooth surface of the measurement gear when the measurement gear is rotated about the rotational axis thereof in synchronization with movement of the gauge head in a direction other than the tangential direction of the base circle; a step of calculating a difference (Δα) between the tooth profile gradient errors that is a difference between the tooth profile gradient error (α1) and the tooth profile gradient error (α2); a step of obtaining a position error (Δx) of the gauge head by using the difference (Δα) between the tooth profile gradient errors and using a gear specification of the measurement gear; and a step of calibrating the position of the gauge head based on the position error (Δx).