DEVICE AND METHOD FOR MANUFACTURING ENDMILL TECHNICAL FIELD The present invention generally relates to a device and a method for manufacturing an end mill, and more particularly to a device and a method for manufacturing an end mill through compression molding. BACKGROUND ART In order to manufacture an end mill from a material having low fonnability and high hardness (e.g., hardmetal cemented carbide), there already exists a technique which manufactures an end mill product by the following steps: molding a powder of material for an end mill into a rod shape through extrusion molding; sintering a molded body to form a blank end mill; and grinding the blank end mill to have a predetermined shape. However, in the above technique, the amount of materials to be grinded is quite large since a blank end mill having a simple rod shape is grinded to have a cutting portion. As a result, there is a problem in that it takes much time to perform a grinding process and the material for an end mill is unnecessarily wasted. DISCLOSURE TECHNICAL PROBLEM It is an object of the present invention to provide a device and a method for manufacturing an end mill, wherein a grinding amount of a blank end mill is small, thereby solving the aforementioned problem of the prior art. TECHNICAL SOLUTION In order to achieve the above object, a device for manufacturing an end mill of the present invention comprises upper and lower punches, a die, a means for supplymg a powder of material for the end mill and a means for eliminating the powder from the top surface of the die. The upper and lower punches are movable up and dovm relative to each other and have a lengthwise molding cavity formed thereon. The die has a penetrating slit sized to be approximated to the width of the upper and lower punches. The penetrating slit allows up-and-down movements of the upper and lower punches. A level of a top surface of the die is configured such that a ratio of a height of a portion for forming the shank portion of the end mill to a height of a portion for forming the cutting portion of the end mill within a space formed by a wall of the penetrating slit and 1 the lower punch corresponds to a ratio of a height of the shank portion of the end mill to a height of the cutting portion of the end mill after molding. The means for supplying a powder of material for the end mill supplies the powder into the space formed by the wall of the penetrating slit and the lower punch. The means for eliminating the powder from the top surface of the die may include a means for sweeping down the powder which is overfilled within the space formed by the wall of the penetrating slit and the lower punch. This adjusts a level of the powder to the level of the top surface of the die. Further, according to the present invention, a cross section vertical to a portion of the lengthwise molding cavity of the upper and lower punches has a semispherical-shaped cavity. Side end portions of the cavity have a radius of curvature (r) different from a radius of curvature (R) of the cavity. A center of the radius of curvature (r) is located outside of the cavity and below a top end thereof. Moreover, the present invention provides a method of manufacturing an end mill, which is capable of achieving the above object. The method of the present invention provides a moldmg device including the upper and lower punches and the die as described above. In addition, the present method comprises the steps of: supplying a powder of material for the end mill into the space formed by a wall of the penetrating slit and the lower punch; eliminating the powder from the top surface of the die; and compression-molding the powder filled in' the space by a relative movement of the upper and lower punches, DESCRIPTION OF DRAWINGS Fig. 1 is a perspective view of a molding device used for manufacturing an end mill in accordance vath the present invention. Fig. 2 is an exploded perspective view of a molding device used for manufacturing an end mill in accordance with the present invention. Fig, 3 is a perspective view of an end mill formed through compression molding by the molding device used for manufacturing an end mill in accordance with the present I invention. Fig. 4 is a perspective view of a lower punch shown in Fig. 1. Fig. 5 is a cross-sectional view of the lower punch shown in Fig. 4, which is taken along the line V-V. BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be exemplarily described with reference to the accompanying drawings so that the present invention can be more easily understood and it can be clearly figured out how it would be implemented. Fig. 1 shows a molding device 1 used for manufacturing an end mill according to the present invention. The end mill molding device 1 comprises an upper punch 3, a lower punch 5 and a die 7. The upper punch 3 and the lower punch 5 have a generally rectangular parallelepiped shape with a thin width. Such punches 3 and 5 are movable up and down relative to each other. A bottom of the upper punch 3 and a top of the lower punch 5 are formed v