To strengthen the function of a heart and lungs withstanding the shortage of oxygen during a horse race by forming atmosphere of proper density of oxygen.

In order to supply a training place 6 consisting of a space 5 surrounded by a top cover 4 and a side wall 3 with gas such as an oxygen gas source 7, a nitrogen gas source 8 and an air source 9 by mixing to 15 to 25% oxygen density suitable for strengthening the function of the heart and the lungs and for promoting restoration from tiredness, a blended gas supplying device 15 with flow rate automatic adjusting valves 10 to 12 connected to each gas of the gas sources and a mixer 13 and the place 6 communicate with each other. Then, an oxygen density set by an oxygen density adjuster 16 is compared with an oxygen density detected by an oxygen density monitor 17 to read a difference between with the set oxygen density to send a signal for adjusting an opening degree to each flow rate automatic adjusting valve of the device 15 to accurately control the oxygen density to supply into the place 6. On the other hand, when the oxygen level becomes dangerous one, an alarm 19 issues an alarm to instruct the device 15 to stop the supply of the mix gas and to supply atmosphere.