To provide a method of making it easy to remove an electron unit in a lead acid storage battery in which the electron unit such as a battery state monitoring unit is fitted and retained in a recessed part installed at a lid of a battery case.

In the lead acid storage battery in which the recessed part is installed at the lid of the battery case and in which the electron unit 5 is fitted and retained in the recessed part, a groove 111 in order to insert a unit removing tool 6 having a protrusion 6b to be hooked to the bottom face 501a of the electron unit 5 at the tip is formed to be extended in the depth direction of the recessed part in an inside face of the recessed part. A dent 112 which continues to the groove 111 and of which one part is opposed to the bottom face of the electron unit 5 is formed in a part closer to the groove 112 of the bottom face 110a of the recessed part, and by this dent, between the bottom face of the electron unit and the bottom part of the recessed part, a gap g in order to receive the protrusion when hooking the protrusion 6b installed at the tip of the unit removing tool to the bottom face of the electron unit is formed.