What is the origin of optical force? In photoelectric effect a photon transfers its energy to an electron. Thus it does some work on an electron and work is always done via some force which in this case called optical force. I want to know what is the nature of this force? As far as I know there are only four fundamental forces. This force cannot be electromegnatic as photon is a chargeless particle. 
 A: Photons are the quanta of the electromagnetic field, so this force is electromagnetic. Electromagnetic fields exerts electric and magnetic forces on charged particles, even though the quanta of the electromagnetic field do not have any charge.
A: In your question you are mixing classical and quantum concepts.
It's correct to say that a photon transfers its energy to an electron. It is not consistent with QFT to speak about work done by the photon. 
Work is a classical concept, based on the concept of force and the possibility of having a path describing the position of the body on which work is done. Both concepts are not at the basis of QFT description. When people speak about four fundamental forces they should rather use the term interaction. I think nobody ever tried to write down a strong force between two nucleons.
Even at the simpler level of Dirac equation, the interaction term  $\bar{\Psi}\gamma^\mu A_\mu\Psi$ cannot be recast in term  work in any meaningful way.
Classical electromagnetic (e.m.) forces are mediated by e.m. fields. But a photon is not something like a small piece of a field. One needs a coherent superposition of many photons to recover the classical picture based on fields and forces between charged particles. 
A: In addition to @G.Smith's answer, the work is of electromagnetic nature and is ultimately done by the system that emitted the photon.
