To develop an automatic detecting system of body temperature of dairy cattle while milking, measurement of the temperature of mammary skin using three thermometers attached into the lining of teat cup was carried out for 23 dairy cattle, whereas measurement of the temperature of milk while milking was also performed for 263 animals. For the latter experiment, three thermometers were attached at 10cm(left and right) and 20 cm away from an individual milk collector on the milk transporting hose. Taking the rectal temperature was accompanied all the time for the experiments. The measurement of the temperature of mammary skin using teat cup was successful for 11 of 23 dairy cattle(47.8%) and the mean temperature was $33.5^{circ}C$ with the mean difference of $5.2^{circ}C$ from the mean rectal temperature. The measurement of the temperature of milk using the thermometers onto the milk transporting hose while milking was very successful , From 37.3 to $38.4^{circ}C$ of rectal temperature, the temperature of milk was almost the same and from 38.5 to $39.5^{circ}C$ of rectal temperature, the temperature of milk tended to be low with the difference of 0.1$^{circ}C$. From 39.6 to $41^{circ}C$ of rectal temperature, the temperature of milk tended to be low with the difference of $0.2-0.6^{circ}C$. These results indicated that automatic detection of body temperature whether low or high can be possible if the temperature of milk is taken while milking and if it is connected to the integration system by on-line.