To melt spin a composite filament without happening troubles related to thermal trouble and insufficient mixing of raw material or the like in extruding a material to a filament.

This device is a melt spinning device including a fiber forming mechanism producing the composite filament by extruding two or more single component strands which are mixed and diluted by a process air after extrusion, enables a proper extrusion by inhibiting an premature leak between two liquid materials and holding optimum temperatures to various kind of liquid materials caused to inhibiting the contact of two or more liquid materials in a spinning pack and separating two kinds of the liquid materials through the spinning pack.