The importance of deep ocean observation has been gradually recognized to understand oceanic effects on the anthropogenic climate change accurately, especially the oceanic heat content and the sea level rise. One suitable device for the observation is a deep float and a monitoring network for deep ocean with many deep floats, which means a deep-ward extension of the Argo, should be built by 2020 as an international consensus of observational ocean sciences. However, there were no floats that can observe the deep ocean below 2,000 m and some institutes and float makers are now developing a deep float. In Japan, Japan Agency for Marine-Earth Science and Technology and Tsurumi-Seiki Co. Ltd. began to develop a deep float, “Deep NINJA,” in 2010, and finally it became available in public in April 2013. Deep NINJA is the first practical float for the deep ocean observation, which can observe the depth up to 4,000 m in the whole ocean except for the area covered by sea ice throughout the year. It is 210 cm in height and about 50 kg in weight with a multi-stage-shaped aluminum-alloy hull. A CTD sensor is attached on the top. The float is designed to have sufficient capacity to load additional sensors, e.g. dissolved oxygen. Bi-directional data transmission of Iridium enables to transfer highresolution data from the float and to change its operation in the sea. The float locations at the sea surface are accurately fixed by the Global Positioning System. The float is driven by lithium batteries to extend its lifetime in the sea, which is estimated at more than 1 year. The article is the former part of the detail explanation on Deep NINJA technologies and it will describe those of the float hardware, especially on buoyancy engine, pressure hull, fixing position, and data transmission.