An electronic control unit includes a control board, a battery pack, and a housing that accommodates the control board and the battery pack. The electronic control unit further includes a battery holder that has a bent shape and includes a bottom surface along a longitudinal direction of the battery pack, the battery holder clamping a main body of the battery pack, and a fixing frame that includes a juxtaposing and mounting part on which a plate surface of the control board and the bottom surface of the battery holder are mounted in a state of being adjacent to each other with a boundary line along the longitudinal direction therebetween, the control board and the battery holder being fixed to the juxtaposing and mounting part. The housing includes an opening portion into which the juxtaposing and mounting part of the fixing frame is inserted, and a back side holding portion that holds the juxtaposing and mounting part at an inner back side of the housing opposed to the opening portion. The fixing frame further includes a sealing front part that closes the opening portion of the housing with the juxtaposing and mounting part accommodated in the housing and that is fixed to the housing in a state of closing the opening portion.