The texture of food in an important physical property in the designing equipment for controlling various food processes and for product quality control. In previous papers 49)50), we studied the simple convenient and cheap textural instrument. This instrument however can not be used for measuring the rheological data of hard materials. Therefore, in the present study we made an improved instrument which can be used for the hard solid foodstuffs. The changes of various physical properties including the rheological value on the soaking and cooking of soybean were investigated. The results by the weighing method which we used in previous paper7) and by the rheological method using improved instrument were obtained in due manner, and the rate equations were postulated by using a nth-ordcr rate equation.