Oil-fired burner, solid fuel-fired burner unit, and solid fuel-fired boiler

An oil-fired burner comprising:

• a nozzle main body which is substantially rectangular in cross-section in a view which is orthogonal to an axial direction of the oil-fired burner;
• an oil gun for inputting an oil fuel disposed at a center of an outlet opening of the nozzle main body;
• a circular diffuser mounted on a leading end side of the oil gun;
• and
• a secondary air input port provided so as to surround an outer periphery of the oil gun, wherein
• the secondary air input port is constituted of:
• a central arc section which is substantially similar in shape to the circular diffuser;
• and
• rectangular sections which are provided continuously from left and right ends of the central arc section in a horizontal direction and each of which has a face-to-face dimension, between a top face and a bottom face, which is reduced from the face-to-face dimension of a rectangular cross-section of the nozzle main body,
• wherein the secondary air input port has an opening shape in which the central arc section bulges out in the vertical direction substantially concentrically with the diffuser, and
• wherein the oil-fired burner is disposed adjacent to an outer periphery of a fuel-fired burner.