To provide an oil supply/discharge device for a fuel injection pump capable of improving work efficiency by making the assembling and removing of a fuel pipe in the unit type fuel injection pump installed for every cylinder and the fuel injection pump itself easily executable at even a time of a work at a narrow place, in particular, and reducing the assembling/removing work man-hour, and assembling and disassembling method therefor.

In this oil supply/discharge device for the unit type fuel injection pump for an internal combustion engine, an injection pump mounting block for every cylinder with an oil supply/discharge chamber formed at the inside is fixed to an engine main body member, the fuel injection pump is attachably/ detachably mounted on the injection pump mounting block, and a fuel supply main passage and a fuel return main passage and an oil supply/discharge block in which a fuel supply passage and a fuel return passage communicated with the oil supply/discharge chamber are formed are fixed to the injection pump mounting block.