To sufficiently support a large load at the collision etc. of a vehicle while preventing assembly stress due to the effects of the vehicle, sufficiently securing its measurement accuracy, and heightening the degree of freedom in installation without increasing layout restrictions.

A seat rail 8 is located between this seat load measuring apparatus 10 and a floor 7 of the vehicle body. Even in the case that assembly stress might occur in the seat load measuring apparatus 10 due to the reception of effects from the side of the vehicle body, the assembly stress is absorbed by a clearance in the sliding splicing of upper and lower rails 11 and 15 in the seat rail 8. Therefore, since the effects from the side of the vehicle body are suppressed in the seat load measuring apparatus 10, its measurement accuracy is sufficiently secured. In addition, since a relatively large load exerted on a seat 1 for a vehicle is supported at a load support means of a base bracket 81 as well, there is no need for increasing the strength of a rear mounting bracket 35, and the rear mounting bracket 35 is compactly formed.