To enable the detection of a surface flaw of a shoulder part from the edge to the surface of a steel plate spring and moreover, a surface flaw in the entire surface of the plate spring.

(1) In this apparatus, magnetic poles 2A and 2B whose upper parts are individually protruded inward are arranged with the radius R of 0.15t-0.45t at the upper end of opposed surfaces thereof and an interval G of t+5-t+40 between the magnetic poles and L-shaped plates 3 each made of a non-magnetic high conductivity material with a bottom part of the L profile formed as flange is arranged respectively on the magnetic poles 2A and 2B with the height H of each flange being 0.2b-0.2b+10. The plates are placed with the flanges upward at positions on the surface flush with the opposed surfaces of the magnetic poles. (2) A driver for adjusting positions of the L- shaped plates 3 may be installed. (3) This apparatus in (1) or (2) as mentioned above and an apparatus by a coil method may be arranged on the same inspection line. A plate spring 1 can be located between the magnetic poles 2A and 2B of the apparatus in the (1) or (2) in a depth of 0.25b-0.35b. (t) and (b) denote the thickness and the width in mm of the plate spring 1.