An experimental device--Thermogradient--for studying the behaviour of small animals under various thermal conditions has been described. Constructive circuit of thermoplates and principal circuits of thermoregulator and test thermometer are given. The device provides using of various combinations of temperature gradients and carrying out prolonged experiments with stable regime of heating and cooling of the thermoplates and the automatic registration of the coordinates of a biological subject on the various recorders. The use of the accessory boxes placed on the necessary number of plates with given temperature gradients is possible.