What is this force?

[celestra]

Electromagnetic momentum according to QM: p=\frac{h}{\lambda}=\frac{h}{c}f
And force is time derivative of momentum: F=\dot{p}
Then, is F=\frac{h}{c}\dot{f}(i.e., electomagnetic wave of which frequency is being increased) can be viewd as a force? What kind of force is this? Electromagnetic force? What is this?

[lalbatros]

Just the usual force.
Note that this is an oversimplified point of view.
The first formula applies for a particle in free space.
To describe a wave when forces are present, a wave equation is needed.
The Schrodinger equation is the basic choice.
The equation you have written cannot replace the real wave equation, altough it can give some insight.
If you are familiar with wave mechanics, read about the WKB approximation.

[Csimmonds]

This is the electromagnetic force I think, as exhibited in the Compton Effect.