An electric fan comprising: an electric motor including: a rotary shaft; a stator including stator magnetic poles; and a rotor including rotor magnetic poles and configured to rotate outside the stator, centering on the rotary shaft; an impeller disposed outside the rotor, the impeller including: an impeller body fixed to the rotor and including an opposed wall portion; and a plurality of blades fixed to the impeller body; one or more bearings for supporting the rotary shaft; and a casing including; a bearing holder by which the one or more bearings are held; and a base including an opposed wall portion opposed to the opposed wall portion of the impeller body in an axial direction of the rotary shaft and extending in a radial direction of the rotary shaft and combined with the impeller body to define a receiving space to receive the stator and the rotor, characterised in that: a clearance is defined between the opposed wall portion of the base and the opposed wall portion of the impeller body to form a labyrinth structure for blocking entry of a liquid into the receiving space from radially outside of the rotary shaft; the opposed wall portion of the base and the opposed wall portion of the impeller body are shaped to form one or more volume expanding portions each having a volume larger than the other portions within the clearance; a groove portion for expanding the clearance is formed in the opposed wall portion of the impeller body, the groove portion extending in a direction apart from the base to define a part of the volume expanding portion; and a groove portion for expanding the clearance is formed in the opposed wall portion of the base, the groove portion extending in the direction apart from the impeller body to define the remaining part of the volume expanding portion. a rotary shaft; a stator including stator magnetic poles; and a rotor including rotor magnetic poles and configured to rotate outside the stator, centering on the rotary shaft; an impeller disposed outside the rotor, the impeller including: an impeller body fixed to the rotor and including an opposed wall portion; and a plurality of blades fixed to the impeller body; one or more bearings for supporting the rotary shaft; and a casing including; a bearing holder by which the one or more bearings are held; and a base including an opposed wall portion opposed to the opposed wall portion of the impeller body in an axial direction of the rotary shaft and extending in a radial direction of the rotary shaft and combined with the impeller body to define a receiving space to receive the stator and the rotor, characterised in that: a clearance is defined between the opposed wall portion of the base and the opposed wall portion of the impeller body to form a labyrinth structure for blocking entry of a liquid into the receiving space from radially outside of the rotary shaft; the opposed wall portion of the base and the opposed wall portion of the impeller body are shaped to form one or more volume expanding portions each having a volume larger than the other portions within the clearance; a groove portion for expanding the clearance is formed in the opposed wall portion of the impeller body, the groove portion extending in a direction apart from the base to define a part of the volume expanding portion; and a groove portion for expanding the clearance is formed in the opposed wall portion of the base, the groove portion extending in the direction apart from the impeller body to define the remaining part of the volume expanding portion.