A diaphragm and a speaker unit which can prevent generation of abnormal sound by suppressing rolling phenomenon. The speaker unit has a diaphragm. The diaphragm includes a portion for supporting a voice coil, and a sound emitting portion formed continuously to one end thereof. The voice coil supporting portion has a shape extending reversely to the sound emitting direction. The sound emitting portion includes a step portion having a surface substantially perpendicular to the sound emitting direction, and a bent portion having a cross-section bent toward the inside of the voice coil supporting portion from one end of the step portion. Consequently, the voice coil supporting portion is movable to describe an arc having a radius substantially equal to the radius of curvature at the bent portion of the voice coil supporting portion and a basic point substantially identical to the center of the bent portion in the bending direction as the voice coil moves in the sound emitting direction or in the reverse direction. Rolling phenomenon can thereby be retarded, the voice coil supporting portion can be prevented from colliding against a magnetic circuit when the speaker unit is driven and generation of abnormal sound can be prevented.