The objective of this study is to investigate the structural behavior of beam-to-column connections where the beam is H-shaped and the column is a box steel member filled with concrete. In general two types of beam-to-column connections with box steel column for rigid joints, one is the inside diaphragm type with hole to fill concrete and the other is the outside diaphragm type have been developed till now. But it is difficult and complicated to apply to high rise building because they have a matter of installation. In this paper, the type of beam-to-column connections which is stiffended by triangular plates is experimented. Simple bending tests are carried out to this type, its strength and stiffness are compared with hollow section type.