An object of the invention is to improve the assembling property of a ring gear and suppress the quality deterioration with a simple structure. To achieve the object, a reduction gear of electrical fishing reel is equipped with: a sun gear (11) disposed at the motor rotating shaft (41)； a plurality of planet gears (12) meshed with the sun gear (11) and supported in a rotatable manner； a ring gear (13) coaxially installed with the sun gear (11) to circumferentially move a plurality of planet gears (12) along an internal gear (131)； a partition wall (46) configured to support a carrier (6) or the motor rotating shaft (41) in a freely rotatable manner and locked at the ring gear (13) in a non-rotatable manner； and a casing cylinder (45) installed at the partition wall (46). The ring gear (13) is received in a rotatable manner at the inner circumferential side of the casing cylinder (45) disposed to be closer to the sun gear (11) side than the partition wall (46). On the ring gear (13), an anti-rotating concave portion (132) is installed at the outer peripheral edge opposite to the partition wall (46). On the partition wall (46), an anti-rotating convex portion (461) locked at the anti-rotating concave portion (132) is installed.本發明的課題係在於能以簡單的構造，提升環狀齒輪的組裝性，並且，可抑制品質降低。用以解決課題之手段為，提供一種釣魚用電動捲線器的減速裝置，其具備有：設在馬達旋轉軸(41)的太陽齒輪(11)；嚙合於太陽齒輪(11)，並且可旋轉地支承的複數個行星齒輪(12)；與太陽齒輪(11)同軸設置，沿著內周齒輪(131)，使複數個行星齒輪(12)環繞移動之環狀齒輪(13)；可自由旋轉地支承載體(6)或馬達旋轉軸(41)，並且不能旋轉地卡止於環狀齒輪(13)之隔壁(46)；及設在隔壁(46)的外殼筒(45)，環狀齒輪(13)係不能旋轉地被收容於外殼筒(45)之較隔壁(46)更靠近太陽齒輪(11)側之內周側，在環狀齒輪(13)，於與隔壁(46)相對向的外周緣，設有防旋轉凹部(132)，在隔壁(46)，設有卡合於防旋轉凹部(132)之防旋轉凸部(461)。
