1. A new apparatus, consisting of a strain gauge and a carrier amplifier, was devised for measuring back muscular and shoulder arms strength by the author. This apparatus was applied for analysing myogenic disorder related to muscular fatigue or pain. 2. Muscular strength with load and its myogram were recorded simultaneously, and their changes during the exertion were analysed. 3. Muscular strength-myograms of sternocleidomastoid muscle, upper trapezius muscle, deltoid muscle, rhomboid muscle and lumbodorsal muscle were observed from the back muscular strength-myogram, and those of teres minor muscle and major pectoral muscle from the shoulder arm strength-myogram. 4. It seemed paradoxically that the amplitude of action myogram increased in proportion to the grade of lowering of muscular strength caused by muscular fatigue or pain.