A wound volume measuring method comprising steps of disposing a foam dressing on a wound site; hermetically sealing said wound site by attaching a film dressing to skin adjacent to said wound site; supplying a negative pressure to the hermetically sealed space formed between said film dressing and said wound site to discharge fluid in said hermetically sealed space; measuring the flow of said fluid discharged from said hermetically sealed space; and calculating, by a volume calculating part, the volume of said wound site on the basis of the measured fluid flow, characterized in that the hermetically sealed space comprises a first hermetically sealed space between the film dressing and the foam dressing and a second hermetically sealed space of the wound site on which the foam dressing is disposed, wherein, when the fluid in the first hermetically sealed space is discharged to reduce the first hermetically sealed space, and the first hermetically sealed space is disappeared, the film dressing is compressed onto the foam dressing, and the step of calculating the volume of said wound site calculates the volume of said wound site by integrating the flow of the fluid discharged in the process that said film dressing and said foam dressing are compressed onto the surface of said wound site, wherein the step of calculating the volume of said wound site calculates the volume of said wound site by integrating the flow of said fluid measured from the time when the measured flow of said fluid becomes smaller than a critical flow, wherein the critical flow is set to a value between a flow (Q' 1) of the fluid discharged in the process that the film dressing is compressed onto the foam dressing, and a flow (Q' 2) of the fluid discharged in the process that the film dressing and the foam dressing are compressed onto the surface of the wound site. disposing a foam dressing on a wound site; hermetically sealing said wound site by attaching a film dressing to skin adjacent to said wound site; supplying a negative pressure to the hermetically sealed space formed between said film dressing and said wound site to discharge fluid in said hermetically sealed space; measuring the flow of said fluid discharged from said hermetically sealed space; and calculating, by a volume calculating part, the volume of said wound site on the basis of the measured fluid flow, characterized in that the hermetically sealed space comprises a first hermetically sealed space between the film dressing and the foam dressing and a second hermetically sealed space of the wound site on which the foam dressing is disposed, wherein, when the fluid in the first hermetically sealed space is discharged to reduce the first hermetically sealed space, and the first hermetically sealed space is disappeared, the film dressing is compressed onto the foam dressing, and the step of calculating the volume of said wound site calculates the volume of said wound site by integrating the flow of the fluid discharged in the process that said film dressing and said foam dressing are compressed onto the surface of said wound site, wherein the step of calculating the volume of said wound site calculates the volume of said wound site by integrating the flow of said fluid measured from the time when the measured flow of said fluid becomes smaller than a critical flow, wherein the critical flow is set to a value between a flow (Q' 1) of the fluid discharged in the process that the film dressing is compressed onto the foam dressing, and a flow (Q' 2) of the fluid discharged in the process that the film dressing and the foam dressing are compressed onto the surface of the wound site.