A power supply apparatus comprising: a battery cell assembly constructed by battery cells each having a positive electrode at one end thereof and a negative electrode at an other end thereof; and a busbar module comprising: a plurality of bus bars configured to connect a plurality of battery cells in series with each other the positive electrode of one of a mutually adjacent pair of the battery cells being connected to the negative electrode of an other of the mutually adjacent pair of the battery cells, a plate disposed upon the battery cell assembly, with the bus bars attached to the plate; and an electric wire holding portion provided on the plate and configured to hold one electric wire of a pair of electric wires (9a, 9b), the pair of electric wires (9a, 9b) each being connected to one electrode (11, 12) of the battery cells connected in series with each other so as to take out a voltage of the battery cells, the electric wire holding portion extending in an arrangement direction in which the battery cells are arranged, and the electric wire holding portion being provided at a central portion of the plate, the central portion being central with reference to a width direction orthogonal to the arrangement direction, wherein the electric wire holding portion includes a wall portion and a first accommodating portion continues to the wall portion upstanding from a plate body of the plate so as to take a box shape defined to be capable of accommodating the bus bar and wherein the one electric wire is disposed in an overlapping manner upon the wall portion and the electric wire holding portion further includes a pair of securing pieces adapted to clamp the one electric wire therebetween. a battery cell assembly constructed by battery cells each having a positive electrode at one end thereof and a negative electrode at an other end thereof; and a busbar module comprising: a plurality of bus bars configured to connect a plurality of battery cells in series with each other the positive electrode of one of a mutually adjacent pair of the battery cells being connected to the negative electrode of an other of the mutually adjacent pair of the battery cells, a plate disposed upon the battery cell assembly, with the bus bars attached to the plate; and an electric wire holding portion provided on the plate and configured to hold one electric wire of a pair of electric wires (9a, 9b), the pair of electric wires (9a, 9b) each being connected to one electrode (11, 12) of the battery cells connected in series with each other so as to take out a voltage of the battery cells, the electric wire holding portion extending in an arrangement direction in which the battery cells are arranged, and the electric wire holding portion being provided at a central portion of the plate, the central portion being central with reference to a width direction orthogonal to the arrangement direction, wherein the electric wire holding portion includes a wall portion and a first accommodating portion continues to the wall portion upstanding from a plate body of the plate so as to take a box shape defined to be capable of accommodating the bus bar and wherein the one electric wire is disposed in an overlapping manner upon the wall portion and the electric wire holding portion further includes a pair of securing pieces adapted to clamp the one electric wire therebetween. a plurality of bus bars configured to connect a plurality of battery cells in series with each other the positive electrode of one of a mutually adjacent pair of the battery cells being connected to the negative electrode of an other of the mutually adjacent pair of the battery cells, a plate disposed upon the battery cell assembly, with the bus bars attached to the plate; and an electric wire holding portion provided on the plate and configured to hold one electric wire of a pair of electric wires (9a, 9b), the pair of electric wires (9a, 9b) each being connected to one electrode (11, 12) of the battery cells connected in series with each other so as to take out a voltage of the battery cells, the electric wire holding portion extending in an arrangement direction in which the battery cells are arranged, and the electric wire holding portion being provided at a central portion of the plate, the central portion being central with reference to a width direction orthogonal to the arrangement direction, wherein the electric wire holding portion includes a wall portion and a first accommodating portion continues to the wall portion upstanding from a plate body of the plate so as to take a box shape defined to be capable of accommodating the bus bar and wherein the one electric wire is disposed in an overlapping manner upon the wall portion and the electric wire holding portion further includes a pair of securing pieces adapted to clamp the one electric wire therebetween.