The present invention provides a loudspeaker diaphragm and an electrodynamic loudspeaker of an elongated shape being shorter in the minor-axis direction than in the major-axis direction, which have a desirable sound reproducing capability with a high efficiency and are not significantly influenced by divided vibrations of an elongated loudspeaker diaphragm, and which are suitably installed in devices such as display devices. In the elongated loudspeaker diaphragm: the diaphragm body includes a first diaphragm portion in a central portion of a rear surface thereof, the first diaphragm portion including a junction to a voice coil bobbin, a second diaphragm portion extending on each side of the first diaphragm portion in the major-axis direction, and a reinforcement rib extending continuously through the first diaphragm portion and the second diaphragm portions; and the edge includes a free edge portion for freely supporting opposite ends in the minor-axis direction of the first diaphragm portion and the second diaphragm portion, and a fixed edge portion being thicker than the free edge portion for fixedly supporting a distal end of each second diaphragm portion in the major-axis direction.