A biochip substrate which is free from cross-contamination due to spot spreading or contact with spots adjacent to each other, and a biochip using the same. A biochip substrate on which multiple valleys for immobilizing biological substances are formed so as to prevent cross-contamination due to spot spreading or contact with spots adjacent to each other, and a biochip using the same are provided. Moreover, it is found out that a desired binding in a target molecule contained in a test sample occurs at a detectable level in a solution system even in the case where a valley have such a small capacity as 1 nL to 10 nL.