Abstract: A portable electronic calculator which has incorporated therein a writing instrument. A miniature electronic calculator is built in a rectangular, elongated body. A cover made of metal covers a control panel for the electronic calculator and a display part, and the cover is mounted on the body to be removable therefrom by sliding the cover in the lengthwise direction of the body. The side marginal portions of the cover are bent inwardly for engagement with both side surfaces of the body to reinforce the body when the cover has been mounted thereon.