To discolor reversible thermal discoloration layers by the heat generated at the time of driving a motor and to enhance the toy characteristic of a toy operated by driving of the motor by arranging heat transfer members in tight contact or proximity to the motor and providing these heat transfer members with the reversible thermal discoloration layers on their surfaces or to a state in tight contact therewith.

Reversible thermal discoloration layers 5 which are black at, for example, <50°C and turn colorless at ≥30°C are mounted to the toy 1 of an automobile, etc., having a pair of contact terminals for receiving the supply of electricity from traveling tracks on the rear surface of a vehicle body and having the traveling motor 2 in the inside in such a manner that the heat transfer members 3 disposed on non- thermally discolorable designs 6 are partly brought into tight contact with the motor 2. The heat transfer members 3 are so disposed so as to constitute part of the armor 4 of the automobile. Thermally insulating covers 8 are disposed on the outside surfaces of the heat transfer members 3 at need to suppress the unnecessary heat loss. When the automobile is made to travel and the motor 2 generates heat, the reversible thermal discoloration layers 5 are changed from black to colorless so that the concealed non- thermally discolorable designs 6 are made visible.