1. A digital camera comprising: a forming circuit unit responsive to a reproduction instruction by an operator for forming a first still image frame corresponding to a monitor frame on a memory; a reproducing circuit unit responsive to said reproduction instruction for reproducing a first still image signal from a recording medium; a writing circuit unit for writing said first still image signal in said first still image frame; a display circuit unit reading out said first still image signal from said memory for displaying a first still image on a monitor, wherein the forming circuit unit is responsive to a synthesizing instruction by said operator for forming a second still image frame smaller than said first still image frame in said first still image frame, the reproducing circuit unit is responsive to said synthesizing instruction for reproducing a second still image signal smaller in size than said first still image signal, the writing circuit unit is configured to write said second still image signal in said second still image frame, and the display circuit unit is configured to read out a synthesized image signal of said first still image signal and said second still image signal from said memory for displaying a synthesized image on said monitor; an updating unit responsive to a moving instruction by said operator for updating a position of said second still image frame, wherein the reproducing circuit unit is responsive to said moving instruction for reproducing said first still image signal, the writing circuit unit is configured to write said first still image signal in said first still image frame, the reproducing circuit unit is configured to reproduce said second still image signal after said first still image signal is written, the writing circuit unit is configured to write said second still image signal into said second still image frame updated by said updating unit, the display circuit unit is configured to read out a synthesized image signal of said first still image signal and said second still image signal from said memory for displaying a synthesized image on said monitor; and a recording unit responsive to a recording instruction by said operator for recording said synthesized image signal on said recording medium.