Force of gravity is least at

The force exerted by the earth on the objects on its surface is given by:
$F=\frac{GMm}{R^2}$

As we can see, the force is inversely proportional to the distance between the object and the centre of the earth which is the radius.
Since our earth has bulged at the equator, the radius is maximum there and hence the gravity is the least. Whereas the radius is the least at the poles, hence the gravity is strong.