Type 88 Small Instantaneous Fuze.This fuze is made specifically for the 50mm Grenade Discharger ("Knee Mortar")
A centrifugally armed fuze with an internal set-back safety.
When fired, the internal arming collar is cycled down and up freeing a set of detent wedge blocks. The projectile's centrifugal force, pushes those blocks out of the path of the firing pin.
On impact the plunger/pin is forced into the primer, detonating the booster.
Upon firing, the arming collar drops and the wedges are pushed out by centrifugal force, clearing the path for the striker.
The text on the label is read right to left.
Loosely translated the top row :
"Model 88, Small, Impact Detonating Fuze".
The last line is most likely the manufacturer's info... Arsenal, Inspector's stamp, etc.