PURPOSE: To maintain the stable circulating performance of the developer by providing a means of holding at least the inside surface of a transport path, which circulates the dry type developer of electrostatic latent images by carrying them in air flow, at the same polarity as that of the charged charge of the developer.

CONSTITUTION: The remainder of the dry type toner used in a developing chamber 2 is carried to a filter 6 together with air by the sucking force of a pump 5 and further it is carried in a circulatory transport path 4 from a storage hopper 3a by riding on its discharge flow. Voltage of the same polarity as the charging polarity of the toner is applied to the transport path 4 from a power source 10 to prevent the toner from depositing on the inside surface of the transport path 4. The transport path 4 is constituted by a conductive pipe or pipe 11 etc. of electrical insulation characteristic having an inside wall 12 with conductive treatment. It is also possible to employ such a material which charges to the same polarity to that of the charged charge of the toner by friction with the toner for the inside surface of the transport path 4. In this case, any material which does not charge as largely as to erase the charged charge intrinsic to the toner is selected.