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 . <EOS>