This part is a kind of semiconductor called RH400.
Function of this product has RH SERIES Controller.
Manufacturers : RKC
Image and pinout :
Some of the text within the PDF file :
RH SERIES
RKC Temperature Controller RH400
Supply : 100 t0 240VAC 50/60Hz
Range : 0-400 celcius
RH100/400/900 ᄽڹ [ ... ]
RH400 PDF Datasheet Download