To realize an inspection method for spark plug capable of accurately determining electrode edge lines facing each other interposing a spark gap in between.
Illumination lights L from a luminous part arranged surrounding an axial line O on the front side in the axial line direction of a central electrode W1 are radially concentrated to the tip end of a spark plug W from the diagonal front outside the central electrode W1 toward the axial line O for illumination to photograph a spark gap part. Since the illumination lights L are introduced diagonally from outside the central electrode W1 to the spark gap (g), strong reflection from the surface of a ground electrode W2 to the axial line direction of the central electrode W1, that is, photographing direction of the spark gap is suppressed and unclear result of edge line image of the ground electrode W2 is suppressed. Also, the illumination light RF1 reflected on the surface of an insulator W4 positioning behind the ground electrode W2 comes to illuminate the ground electrode W2 from the back and so the edge line of the ground electrode W2 can be clarified owing to a silhouetting effect.
NOZAWA KAZUHIRO
KOUMATSU SHINICHIRO
ODAGIRI AKIRA
NASUNO MASARU
TAKANO CO LTD