A manufacturing apparatus of a spark plug, comprising: a holding unit adapted to hold a workpiece, the workpiece having a shape extending along a center axis thereof and including a metal shell part to be processed into a metal shell of the spark plug and a ground electrode part to be processed into a ground electrode of the spark plug; a feeding unit adapted to feed the workpiece to the holding unit; dies for working the workpiece to form a thread portion on an outer circumferential surface of the metal shell part; a position measurement unit adapted to measure a position of the ground electrode part in a state where the workpiece is held in position by the holding unit; a die control unit adapted to control working of the workpiece with the dies; where the ground electrode part is located on one end side of the workpiece at a position displaced from the center axis of the workpiece; the dies are capable of changing a working phase of the dies relative to the workpiece; the position measurement unit is configured to measure the position of the ground electrode part in a non-contact manner; and the die control unit is configured to control the dies to adjust the working phase of the dies relative to the workpiece based on the measured position of the ground electrode part and then effect working of the workpiece with the dies; characterized in that: the feeding unit is configured to feed the workpiece to the holding unit in a state where an orientation of the workpiece is corrected with respect to a predetermined direction; and the non-contact manner to measure the position of the ground electrode part comprises emitting laser light to the ground electrode part from a direction perpendicular to the center axis of the workpiece. a holding unit adapted to hold a workpiece, the workpiece having a shape extending along a center axis thereof and including a metal shell part to be processed into a metal shell of the spark plug and a ground electrode part to be processed into a ground electrode of the spark plug; a feeding unit adapted to feed the workpiece to the holding unit; dies for working the workpiece to form a thread portion on an outer circumferential surface of the metal shell part; a position measurement unit adapted to measure a position of the ground electrode part in a state where the workpiece is held in position by the holding unit; a die control unit adapted to control working of the workpiece with the dies; where the ground electrode part is located on one end side of the workpiece at a position displaced from the center axis of the workpiece; the dies are capable of changing a working phase of the dies relative to the workpiece; the position measurement unit is configured to measure the position of the ground electrode part in a non-contact manner; and the die control unit is configured to control the dies to adjust the working phase of the dies relative to the workpiece based on the measured position of the ground electrode part and then effect working of the workpiece with the dies; characterized in that: the feeding unit is configured to feed the workpiece to the holding unit in a state where an orientation of the workpiece is corrected with respect to a predetermined direction; and the non-contact manner to measure the position of the ground electrode part comprises emitting laser light to the ground electrode part from a direction perpendicular to the center axis of the workpiece. the feeding unit is configured to feed the workpiece to the holding unit in a state where an orientation of the workpiece is corrected with respect to a predetermined direction; and the non-contact manner to measure the position of the ground electrode part comprises emitting laser light to the ground electrode part from a direction perpendicular to the center axis of the workpiece.