Atomic images of the Bi–O and Cu–O planes were selectively observed in STM experiments on slightly underdoped Bi 2 Sr 2 CaCu 2 O 8+δ by changing bias voltage, and tunneling spectra were measured while observing the Cu–O plane at three tip heights ( h 1 > h 2 > h 3 ). The Cu–O plane images indicate that the conduction holes go mainly into O 2 p σ and Cu 3 d x 2 - y 2 orbitals. The spectra for h 1 and h 2 are consistent with a gap having lines of nodes at the directions 45° from the Cu–O bonds, as shown in our previous work. On the other hand, the spectra for h 3 , where the tip seems to be very close to the specimen surface, are quite similar to expectations for the pair-breaking due to non-magnetic impurities in a d -wave superconductor. This, combined with the result for the node directions, strongly supports a d x 2 - y 2 superconducting gap.