This paper presents a microfluidic device that geometrically constrains the development of individual Dictyostelium discoideum cells into multicellular organisms (slugs). A microchip for the stimuli-directed migration of slugs is also presented. To demonstrate the formation of slugs in a predetermined shape, a microchip is designed to confine the slugs in the vertical direction. In the microchip, sufficient oxygen is supplied to the cells via a membrane, allowing the formation and adaptation of slugs to the shape of the channel. In addition, the manipulation of slug migration direction in a microchip via external stimuli, such as light and temperature gradients, that induce phototaxis and thermotaxis of slugs, respectively, is demonstrated. To direct slug migration with external stimuli, an optical fiber is used for phototaxis and an electrical wire heater is used for thermotaxis. Experimental results show slug formation in a predefined geometry in the microchip, suggesting that this chip is potentially useful for understanding the relationship between the shape and function of cells or tissue. The controlled migration of slugs demonstrated in the microchips can potentially be employed in biologically based microactuators or microrobots.