A watertight fixing portion 65 as a peripheral portion to be watertightly fixed to the base portion 45, a top portion 66a formed to have a first height H1 at which the finger hold portion 59 does not contact when the shaft member 55 is tilted to a predetermined angle An outer circumferential wall portion 66 rising from the watertight fixing portion 65 toward the inner circumferential side of the valley portion 67 toward the inner circumferential side of the outer circumferential wall portion 66, a valley portion 67 continuing from the inner circumferential side of the outer circumferential wall portion 66, An inner peripheral wall portion 68 which rises to a second height H 2 higher than H 1 and a central portion which is connected to the inner peripheral side of the inner peripheral wall portion 68 and is fixed to the bending operation lever 47, And closes the opening 45 a of the base portion 45 watertightly by using such an elastic cover 48.ベース部45に水密固定される周縁部としての水密固定部65と、軸部材55を所定の角度θまで傾倒したときに指当部59が接触しない第1の高さH1に形成される頂部66aに向けて水密固定部65から立ち上がる外周壁部66と、外周壁部66の内周側に連設された谷部67と、谷部67の内周側に連設されて第1の高さH1よりも高い第2の高さH2まで立ち上がる内周壁部68と、内周壁部68の内周側に連設されて湾曲操作レバー47に固定される中央部と、を備えて弾性カバー48を構成し、このような弾性カバー48を用いてベース部45の開口部45aを水密に塞ぐ。
