This paper is intended as a consideration of prot-axonometric projection on“Bellicorum instrumentorum liber” (1418-ca.1420) of artist-engineer's Giovanni Fontana in Early Renaissance Padua. I consider the subject under the following heads : (1) the analysis of the 25 figures based on prot--axonometric projection, (2) the consideration of the drawing method of Fontana. These analysis lead to the conclusion that 1) Fontana used the 4 type of the prot--axonometric projection which is a) “Parallel”, b) “V Shape”, c) “Parallel-V shape”, d) “V shape-Parallel”. 2) The drawing of “V Shape” base on medieval optics. 3) The drawing of “Parallel-V shape” is followed Valturius's “De re militari” as the drawing method for engineer.