kchaiyan

It's a female Pied Harrier. Note faint underwing barrings and silvery grey upperwing, esp secondaries, and visible on the bird at perch and closed wing.

Female Eastern Marsh Harrier should be considered, as wgeoff pointed out, but can be excluded because underwing barrings will be more obvious and upperwing on secondaries will be dark brown.  Also the rump is barred pale, as opposed to very outsandingly white in female Pied.