To form a long head by combining a plurality of short heads, thereby enabling high speed ejection, to simplify the structure and to improve the yield and the maintenance property.

There is disclosed a liquid droplet jet head in a long head constituted such that a plurality of short head modules each having ejection nozzles for ejecting liquid droplets are built in a base substrate. The liquid droplet jet head comprises a common liquid channel for supplying a liquid to each of the short head modules which are formed on the whole region of the base substrate in the longitudinal direction thereof and a positioning mechanism for detachably attaching the head modules to the base substrate.