In an exercise machine, when a measurement starts, an electrocardiographic signal is detected by an electrocardiographic sensor 1 (ST33), a load drive is started (ST4), and heartbeat rate intervals of the electrocardiographic signal are sequentially obtained. A fluctuation of heartbeat rate intervals PI(n) % is obtained from a calculation formula in which the RR interval RR(n+1) of the current heartbeat is subtracted from the RR interval RR(n) of the previous heartbeat, which is then divided by RR(n) and multiplied by 100% (ST5). Entropy is calculated from 128 pieces of such PI (ST6). From the change of the entropy under the gradually increasing load (ST8), a minimum point of the entropy is obtained, which point is designated as an anaerobic threshold point (ST7). The load of the exercise machine is controlled employing this anaerobic threshold.