AI techniques are required for realizing society 5.0. For the issues of societal implementation for AI, an AI hardware, which is enhanced security performances including authentication, and so on, is needed in order to reduce security risks. This study proposes a new physical unclonable function (PUF) based on neural network (NN) called NN PUF. The proposed NN PUF uses a difference of calculation time in NN due to production variations of semiconductor. Evaluation experiments using a field programmable gate array (FPGA) prove the effectiveness of the proposed NN PUF.