The plasma apparatus includes a conveying unit for conveying a substrate in a conveying direction while being situated at a processing position, an elongated electric field forming unit for forming an induction electric field by a coil, opposed to the processing position, a power supply for supplying high frequency power to the coil, an elongated gas introducing unit and a separating unit for separating a region where the forming unit is arranged and a region where the introducing unit is arranged from each other in an airtight fashion, having an elongated dielectric window arranged between the processing position and the forming unit. The forming unit, the introducing unit and the dielectric window are arranged in such a way that there longitudinal directions are matched with a width direction of the substrate being conveyed, and orthogonal to the conveying direction.