To provide a seat load measuring apparatus which sufficiently supports a large load at the collision etc. of a vehicle while enhancing the degree of freedom in installation without increasing layout restrictions.

When an upward load is exerted on a seat rail 8 in normal times, since the load is relatively small, it is sufficiently supported by a rear rail bracket 35. When a large load at the collision etc. of the vehicle is exerted upward on the seat rail 8, a semicircular part 81a1 of a load support member 81 comes into contact with a stopper bolt 24 to sufficiently support the large load by the load support member 81. There is thereby no need for increasing the strength of a section α of the rear rail bracket 35 at which a hole 38 is formed. As a result, there is no need for increasing the size of the section α at which the hole 38 is formed.