IN recent years, mice bave been used widely as one of the important pointing devices of a computer. The mouse which has high performance and multiple functions is required in order to improve the usability of a computer. Some researches which add a tactile display function to a mouse have been done, and mice with the tactile display using a vibrator have been put on the market. However, acoustic noise generated by the vibrator make its user uncomfortable. Then, this article proposed and developed a new tactile display mouse using passive and fail-safe device called ERG (Electro-rheological Gel). First, the characteristics of ERG were measured through some experiments. From the results, it is found that the stiffness of ERG is an electrically controllable characteristic when ERG and electrode is sliding. Then the device was incorporated into the click button of a mouse and evaluated through some identification tests by some human to identify the button's stiffness. In shortly, identification rate was over 90%. Consequently, the developed tactile display can successfully express multi-level of tactile senses. Finally some application of the tactile display also proposed.