To efficiently and inexpensively realize the insulation of a retaining fitting for tightening an on-vehicle battery in a device for fixing the battery.

This battery fixing device is provided with a floor member 32 for forming a loading face of the battery 60, a supporting member 33 for locking one side face in the left and right directions of the battery 60 loaded on the floor member 32, a positioning member 34 for regulating the battery 60 in the forward and backward directions of a vehicle, the retaining fitting 36 abutting on an upper side corner part of the battery, and a means 37 for tightening the retaining fitting 36 in the direction for generating component force in two directions for holding down the battery 60 between the retaining fitting 36 and the floor member 32 and between the retaining fitting 36 and the supporting member 33. Coatings 55, 56 formed so as to wrap a part abutted on the battery 60 of the retaining fitting 36 by coating of an insulation material are provided. Sliding-off prevention parts 55a, 56a formed by an insulation material for burying holes 57, 58 of the retaining fitting 36 are provided on inner sides of the coatings 55, 56.