A plasma irradiation device (20, 220, 420, 520, 620) provided in a handpiece (3, 203, 303, 403, 503, 603) including an acting member (31, 212, 312, 535) which acts on biological tissue, comprising: a gas flow channel (22, 222, 522) for supplying to a distal end portion of the acting member (31, 212, 312, 535) a gas supplied externally of the handpiece (3, 203, 303, 403, 503, 603); and an electric field generation section (30, 230, 530) disposed in the gas flow channel (22, 222, 522), the electric field generation section (30, 230, 530) including a first electrode portion (31, 231, 531), a second electrode portion (32, 232, 532) facing the first electrode portion (31, 231, 531), and a dielectric member (40, 240, 540) having at least a portion which is located between the first electrode portion (31, 231, 531) and the second electrode portion (32, 232, 532) and is disposed on at least one of a surface of the first electrode portion (31, 231, 531) and a surface of the second electrode portion (32, 232, 532), the electric field generation section (30, 230, 530) is configured to generate an electric field in a space within the gas flow channel (22, 222, 522) by using a potential difference between the first electrode portion (31, 231, 531) and the second electrode portion (32, 232, 532), thereby producing the low-temperature plasma discharge, characterized in that the dielectric member is configured such that the portion located between the first electrode portion and the second electrode portion is in contact with both the surface of the first electrode portion and the surface of the second electrode portion; at least a portion of the dielectric member forms an inner wall portion of the gas flow channel; and the low-temperature plasma discharge is produced along the inner wall portion. a gas flow channel (22, 222, 522) for supplying to a distal end portion of the acting member (31, 212, 312, 535) a gas supplied externally of the handpiece (3, 203, 303, 403, 503, 603); and an electric field generation section (30, 230, 530) disposed in the gas flow channel (22, 222, 522), the electric field generation section (30, 230, 530) including a first electrode portion (31, 231, 531), a second electrode portion (32, 232, 532) facing the first electrode portion (31, 231, 531), and a dielectric member (40, 240, 540) having at least a portion which is located between the first electrode portion (31, 231, 531) and the second electrode portion (32, 232, 532) and is disposed on at least one of a surface of the first electrode portion (31, 231, 531) and a surface of the second electrode portion (32, 232, 532), the electric field generation section (30, 230, 530) is configured to generate an electric field in a space within the gas flow channel (22, 222, 522) by using a potential difference between the first electrode portion (31, 231, 531) and the second electrode portion (32, 232, 532), thereby producing the low-temperature plasma discharge, characterized in that the dielectric member is configured such that the portion located between the first electrode portion and the second electrode portion is in contact with both the surface of the first electrode portion and the surface of the second electrode portion; at least a portion of the dielectric member forms an inner wall portion of the gas flow channel; and the low-temperature plasma discharge is produced along the inner wall portion.