Mechanical apparatus for demonstrating trigonometric circle and the Sin, Cos, Tan and Cot functions, comprising : a board with a circle and coordinate axes drawn on , with the origin is at the center of the said circle ; A construction of rigid bars and sliding perpendiculars, could be moved electrically or by hand, form with the said circle and coordinate axes: a Point (D) as an arbitrary point on the circle, with (B) as the projection of (D) on the X- axis, (F) as the projection of (D) on the Y- axis, (G) the angle corresponding to the point (D). Installed bar as tangent or cotangent line to the circle to represent the Tan and Cot of (G). So (RB) represents Cos G, (RF) represents Sin G. This apparatus will show in easy and clear way the characteristics and properties of Sin, Cos, Tan and Cot functions . Other concepts could be demonstrated by the same construction, as concept of arc, radian etc, also the said construction could draw the graphs of the mentioned functions through a system including pens and papers.