We have invented mobile HEPA filter unit of hemopoietic stem cell transplantation clean room (class 100), which is a capsule type to protect the patient from being infected by harmful Aspergillus spore. This equipment is based on the basic structure of US Federal Standard 209D, biological clean room standard of NASA NHB 5340-2 and measurement standard of Japanese JACA No. 24-1989. Performance of HEPA filter was evaluated by dioctyl phthalate (DOP) test method, resulting in 99.97% efficiency for 0.3 ㎛ particles. HEPA filter unit used only 98 W electricity with 24 V storage cell for the patient's treatment for over three hours. When the wind speed was 0.2 to 0.3 m/sec as in bone marrow transplantation clean room, the air flow was constant laminar vertical type. When the amount of dust was measured in the hospital, the equipment maintained the grade of clean class 100 and microbe was not detected. The noise level was less than 52 dB(A). The amounts of microbe inside and outside the building were almost same. The amount was even more in cancer sick room, serious case room and X-rays room than in the general rooms. Also, elevators and stair room were found to transport dust to other areas. Even though the patient with low immunity can be protected from Aspergillus spore by a HEPA filter unit, the system preventing microbe system such as BMT clean room should be placed in rooms such as PET, CT, MRI, and radiation room so that the patients can be protected from having infected by the extremely harmful Aspergillus spore.