A method for detecting a rare cell having a possibility of being contained in a cell suspension, from the cell suspension by the use of a cell-spreading device, said cell-spreading device comprising: a microchamber chip having, on its surface, two-dimensionally arranged microchambers capable of enclosing and retaining a cell, a channel-forming frame that is united with the microchamber chip so that a channel is formed on the microchambers, an inlet provided in the channel-forming frame in order to allow a cell suspension to flow into the channel, and an outlet provided in the channel-forming frame in order to allow the cell suspension, which has been allowed to flow into the channel through the inlet, to flow out from the channel, wherein the "void ratio" that is a ratio of the sum total of voids to the longitudinal width is not more than 5%, said void being a length obtained by subtracting a width corresponding to a projected aperture of the microchamber from a longitudinal width, the projected aperture of the microchambers being given by projecting the aperture of the microchambers perpendicular to a direction of the longitudinal width of the microchamber chip, said method comprising: a step of introducing the cell suspension into the channel through the inlet of the cell-spreading device to spread cells on the surface of the microchamber chip, and a step of enclosing the spread cells in the microchambers, with a plurality of cycles of an intermittent liquid sending in which the cell suspension is sent through the inlet and thereafter allowed to stand still for a predetermined period of time in one cycle. a microchamber chip having, on its surface, two-dimensionally arranged microchambers capable of enclosing and retaining a cell, a channel-forming frame that is united with the microchamber chip so that a channel is formed on the microchambers, an inlet provided in the channel-forming frame in order to allow a cell suspension to flow into the channel, and an outlet provided in the channel-forming frame in order to allow the cell suspension, which has been allowed to flow into the channel through the inlet, to flow out from the channel, wherein the "void ratio" that is a ratio of the sum total of voids to the longitudinal width is not more than 5%, said void being a length obtained by subtracting a width corresponding to a projected aperture of the microchamber from a longitudinal width, the projected aperture of the microchambers being given by projecting the aperture of the microchambers perpendicular to a direction of the longitudinal width of the microchamber chip, said method comprising: a step of introducing the cell suspension into the channel through the inlet of the cell-spreading device to spread cells on the surface of the microchamber chip, and a step of enclosing the spread cells in the microchambers, with a plurality of cycles of an intermittent liquid sending in which the cell suspension is sent through the inlet and thereafter allowed to stand still for a predetermined period of time in one cycle. a step of introducing the cell suspension into the channel through the inlet of the cell-spreading device to spread cells on the surface of the microchamber chip, and a step of enclosing the spread cells in the microchambers, with a plurality of cycles of an intermittent liquid sending in which the cell suspension is sent through the inlet and thereafter allowed to stand still for a predetermined period of time in one cycle.