An image forming apparatus having a developing unit including a plurality of units. The limiting part includes a pair of link members that engage with each other, one ends of the link members rotatably supported by the base portion, and the other ends thereof slidably supported by the operable member. A detection coil 2 disposed between the excitation coils 1a, 1b detects bypass eddy current D which flows in the circumferential direction of the test object 31 while bypassing a circumferential crack E. Packages produced from such films demonstrate balanced tear start and tear propagation properties in the crosswise and lengthwise direction of the film. The outer side of the unit is smooth and is designed to receive identifying or advertising indicia. A portion of the joist in the backspan region comprises a decking supporting member coupled to the web between the upper chord and the lower chord.