Flyback converter primary and secondary sides power calculation
For ideal case, is it correct that power at primary winding is equal
  to the power at secondary winding, and that is the equation for this
  power.


With ideal switches and diodes, zero transformer losses and switching losses and 100% transformer coupling, yes, all of the net energy taken by the primary winding is transferred to the secondary winding in the 2nd part of the switching cycle and that net energy multiplied by the switching frequency equals the power transferred.